I recently start re-read my books and stumble a little with Folk Witch tradition (from Hedge Magic 5e).
And I probably miss something, because they look, well, too weak - even compare to other traditions from some book.
Their fetishes require vis and season for creation (and not give any bonuses for casting). Potions eat a lot of vis.
It's look like their main thing is creating heal and mana potions for mages (like whole ability for this).
So, I probably miss something. Can anyone help me
Whatever is the point of any tradition, really? They fill in a specific niche and/or represent a certain "mythical identity" of magicians that medieval Europe conceived of. Order of Hermes and the Hermetic Magi? Closest they get to the Merlin-esque archetype.
Most Hedge Wizard traditions though are based on some medieval folklore or another and are more rooted in it. Folk Witches represent an amalgam of those beliefs, witches that cast and brew benign and malevolent magics, have small familiars, can fly or otherwise shapeshift themselves. So, they can fit neatly into most areas as obstacles or potential allies to an individual magus or covenant.
Now, if you mean what their mechanical niche is...
They can instantly restore wounds (something that would usually require at least an hour to magi) for slightly less vis, can store that power with potions, and can restore fatigue, something Hermetics can't do at all. The matter of vis affects them the same way it affects Hermetics - pending on how rich the area is.
They can Shapeshift, and while yes, this requires a Fetish, it is really no different from Magus having to invent a spell to transform. Tradeoff is that they can confer this ability on others with potions. Likewise, Shapeshifting does not care for Parma Magica so they can still maul or poison an unwitting Magus. Speaking from personal experience, it's all fun and games until a village loyal to a coven turns into a troop of bears who don't care for your Parma and are out for blood.
Potions can get much higher penetration than usual Supernatural Ability spellcasting total, and the cursing fetishes can last indefinitely if they punch through. A cursing witch is likely to be good with Penetration anyways, and Dowsing combined with Shapeshifting ensures that they can find pieces of you and gather them discreately if need be.
So OP has a point in that the folk witch's forte tends to benefit the rest of the troupe more than themselves. That makes them less fun to play in a power contest, or rollplaying game, but no less rewarding in a roleplaying game.
I am not sure the other hedge traditions have more to them. Played as unGifted companions, they soak up virtue points on an extremely narrow skill set. Played in the magus slot, they are just weaker than Hermetic magi, and they are left out of the thrills of Hermetic politics on top. But as the previous poster points out. They fill a role in the mythic tapestry, and are worth playing just to complete the mythic illusion.
Well, while they do miss out on Hermetic Politics, there is always the Sabbat Politics and if it is true, the Grand Sabbat.
If you're willing to play a Hedge Wizard game, or have an Ex Miscellanea from said tradition.
I mean Cunning Folk cover big share of "representation" part of Folk Witches. If I read it right, they can even made trick with troop of bears (but probably more preparation).
I think inventing spell to transform vs build fetish is very big difference, or two. First Magus don't lost spell this easy. Second - reserach spell don't eat vis.
I think for it's more about Folk Witches was relatively in "their" area (and I probably dislike Healing, because Mystic Herablism IMO fit their "story role" better). Well, and maybe I think something like Muspelli rituals fit them better - untied from seasons work and can fill most of Cursing thing.
When I write question, I think that I miss something, but look like it's more about point of view.
Folk Witches are classic folklore/fairy-tale witches. That's why they exist - so they can fill that niche.
They are somewhat weak compared to many other hedge traditions. But nobody said those all have to be equal in power.
Some will find Folk Witches fun to play. And they make excellent NPCs.
And, munchkinistically speaking, fantastic grogs 
Having played both a Folk Witch and a Cunning Folk, yes they are both capable of playing the role of the "witch-in-the-woods", but neither would fit in all areas. I find regional variance to be more interesting, and as is the case with most magical aspects of Ars Magica - there is more ways than one to fill a cup with water.
Inventing a spell, enchanting a lesser enchantment or creating a fetish, doesn't matter really - all 3 take you a season of work, and latter two will cost you vis. Some Covens of Folk Witches ignore the usual restriction on shared fetishes (like the Basque Sorginas).
As for the research not costing them vis, true. All traditions will have their pros and cons. Few will have the sort of flexibility Hermetics do, and most will be better in some specific field than them or violate some limits of Hermetic Magic. In case of Folk Witches, that is Healing, they're in most scenarios, better at it.
Now, compared to Folk Witches, yes Learned Magicians / Cunning Folk do have a wider arsenal, and can generally very quickly respond to most situations with something more quickly, even if its a rather minor form of magic. They're fairly good as court wizards or adventuring magicians you could say. But in my experience, they will struggle to attain higher-end magic (verbal or via chartae) unless you really specialize them in respective fields and they will still struggle with Penetration. Bear gambit for them would be far less effective - higher magnitude magic, which must account for Penetration, as its a Magicam Charm / Chartae rather than the real deal. Folk Witches also have a Hedge Magic Theory so they can actually do research into stuff right off the bat, which they also seem to use for their Initiations IIRC.
One more thing that's really important about Folk Witches is that they can initiate the unGifted, whereas Magi must be gifted. There is a hard cap on how many people have The Gift (1 in 10,000 people, iirc; can't check my book because the cat is on my lap). Because you can initiate theoretically anyone, a dedicated Folk Witch Coven (with, admittedly, good PR, funding, and someone with ironclad logistics skills) could create as many mages as there are in any given Tribunal in about a decade. Assuming they were going hard at it, with each wave of initiates training up to initiate another set after ~10 years, the exponential growth would allow for a comparable number of Folk Witches as there are Hermetic Mages within a generation or two.
Now, I cannot imagine that this is the most practical approach to any given problem, but I can see how someone with a grudge who wanted to bring an army of witches down upon the Marcher Lords of Powys; or someone with a benevolent dream who wanted to have a Witch Healer in every town, could decide to get it going.
Moreover, I think it's important that there be many routes to power in the setting - people born with it, and people who come to it the hard way. Folk Witches are a good model for the latter.
I think that this is an easily overlooked advantage. It also means that Folk Witches could acquire other Supernatural Abilities easier than most hedge traditions -- by seeking out other Folk Witch lineages that have a slightly different list of favored abilities. Maybe use one of their initiation scripts, or do integration research if the other tradition isn't that compatible.
I think this is their core strength. I also think that in ME they could end up playing the trigger of the inquisition ramp-up.
Afterall, they are less powerful than hermetic Magi. They are as much susceptible to wanting more power than they have and the infernal is willing to provide.
W
True, the situation in a hedge game and an Hermetic saga are hardly comparable. I really only considered the Hermetic saga.
In an Hermetic game, there will not be time to play out the politics of every non-Hermetic tradition represented.
Ars majica says "Game balance. What is that?". For example, a +3 virtue, gives double the XP of a guy with a -3 flaw (Rich vs poor). It's one of the key differences between Ars Majica and other systems. Some characters are weaker. Whatever +3 virtue one can buy to offset poor, it is not good enough to recover from how much poor nerfs someone. It is about the story involved with playing a poor character.
The order is the pre-eminent magical tradition. Arguably hermetic magic was better than most to start with. Add hundreds of years of concerted effort improving the original hermetic magic of Bonisagus and the active suppression of other traditions; other traditions should be weaker, with a few niche elements they are good at.
I disagree!
A Poor, Great Noble (LoM p.31) may have less experience overall because he spends so much time administering his estates... but he commands a range of Abilities "embedded" in his vast force of servants, spies, minstrels, knights etc. worth far, far more xp than any single character can have on his own
Folk Witches make excellent antagonists for "who stole from the vis source?" or "why are there no magical animals of the sort I want for a familiar?" as they compete with the hermetic magi for resources. Their ability to curse can create magical mysteries to investigate. They can have a group of witches on broomsticks drop things from a great height to threaten people.
There are a lot of uses for Folk Witches. The hedge tradition I have difficulty comprehending is Nightwalkers - I think I need to see one in play or be in a scenario with a clever Nightwalker antagonist to understand.
Well, I don't even compare Folk Witches to Order. Only to another hedge groups.
Like Cunning Folk, who share some "ecological niche", but seem having more instruments.
where are the rules for cunning folk? I only find them in 4ed.
I do not see how folk witches come up poorly compared to other traditions in the same book. They have some pretty hefty powers, as have been mentioned. Their healing is pretty unique and vis efficient, and fatigue restoration even more unique. Shapeshifting is also a convenient and easy-to-use field power. Dowsing and second sight are also very versatile and often requires a large repertoire of spells to replicate with Hermetic magic. By comparison, it is very difficult to make a starting vitkir with useful field skills. A learned magician, as far as I have seen, is just a feeble wannabe Hermetic. Gruagachan have some hefty powers, but I find them a lot hard to make useful on stage.
Cunning Folk are a reskin of Learned Magicians, and described in the same chapter.
I feel like Nightwalkers are like hackers in cyberpunk games: they undoubtedly do some very cool things, but it's hard to integrate them into anything other characters want to do.
But like Folk Witches, I think they get a lot of their justification from being taken from actual medieval beliefs.