"What story benefits can you gain by using the research into creating a regio?"
I am a bit incredulous that a person can't see the advantage of creating a regio...
If a person can create one, then the next step is determining it's strength.
Combined with the difficulty for a non-native to find such a place, Magi could easily say. buy a house smack in the middle of town, blossom a massive regio inside at any level they like, and walk-in. Since mortals under normal; circumstances can't get in, the Magi have now set up a home right in the middle of a major population center that is actually VERY well protected from the common rank and file.
Imagine the boon to the Order of someone walking all those old roman roads, and just popping up regio's for the Order say every 20 miles along the road length?
Putting just a bare smidgen of consideration into the sheer enormous advantage of the ability to create a regio(on purpose), much less an aura... it can get mind-boggling.
As to the question. Yeah, I had an NPC several hundred years old as a Magi, a Mernita no-less, who delved in chthonic dark magics(before we had the real stats for that form of magic) discover the ability to make Regio's, but it drove him appropriatley mad in the proccess, and he was almost totally unable to repeat the feat.
The players ultimately were forced into a new Schism War between the Chthonic cults of the Order and the Order itself as they found out the regio's being one-time created by the Chthonic magic followers were cysts between this world, and the worlds of greater older beings who wanted to destroy all life here.
They learned SOME tricks about shrinking and growing regios, even manipulating the strength of Regio's, but never how to bold out create one. Two even died for delving too far into Chthonic's to learn the secrets.
The order's ultimate answer to the new Schism War was a newly formed ritual similar but far more powerful than the one used on the Diedne. They sacrificed some of thier own(who went willingly) to empower a spell that would latch on to the Chthonic taint, and amplify that Taint out of the tainted individuals control, until they quite literally exploded. Which of course killed the two players characters who went too far.
Of course a few got away.... by hiding in other realms, like making deals with Arcadia.
More modern versions taking place after 1270 in my Ars Games even have a modified code treating any Magi caught using Chthonic magic the same as any magi getting caught having dealings with Demons.