As Erik Tyrell rightfully reminded us, spell guidelines are guidelines not rules. In fact, spell design leaves a number of areas to the appreciation of the storyguide for balance.
In Ars Magica, requisites come in two forms: Spell Requisites, which apply both to lab totals and to casting totals, and Casting Requisites, which only apply to casting totals. It is generally easy enough to determine when a spell requisite is necessary, but there are few enough examples of casting requisites to guide spell designers:
Transformation and teleport spells allow casting requisites to cover the Form of carried objects.
Generic "telekinesis" ReTe spells require casting requisites to cover the Form of the lifted objects.
What are your own guidelines when deciding when a spell should allow or require casting requisites, as opposed to spell requisites?
The tranformation, teleportation and telekinesis criterea that you mention are the only instances that come to mind when I've used them.
I never use casting requisites for imagonem spells.
They're apparently unneeded for vim spells (although many vim spells are form specific).
Here's a question that I've had; suppose that I have a casting tabet for a spell that requires casting requisites. Do these requisites need to be specified when the casting tablet is created or not?
If the spell could function Without the requisite, or if the requisite does not apply in all circumstances, then I would call it a mere Casting requisite and would not interfere with the lab total. For example, generic ReTe "telekinesis spells", which require an Herbam casting requisite if you want to pick up that board, or no requisite at all if moving some stones.
Spells that cannot function in any way without the requisite have the requisite applied to their lab total as well as casting, such as a Muto spell to change a person to a toad.
I myself do not require any sort of requisite for teleportation. Too much of a pain.
Even though I understand that RAW indicates the use of casting requisites if you want to teleport your iron weapon, paper scrolls and wool clothing along with you, but I agree with Marko in not using those requisites for most teleport spells.