The major downside of derived roles is that the will all be exactly the same, except for technically defined org level fields.
My understanding is that Anwer wants them to be almost the same and not exactly the same. So sending a set of different non-org fields to the one company without being forced to upgrade the field makes sense. Using one company as a pilot for new transactions might make sense as well. Eventually one comes to the conclusion that derived roles are actually a pest.
I dont use them.
Cheers,
Julius