Squire powers. If you're in Fortress, you're not hiding it, usually. However, every other cabal gives you at least more than one useful cabal power. As a Squire/Acolyte, you basically get for free a really easy-to-find prep that could be replaced in a few short moments.

You don't join cabals just for powers, but they're useful for every other cabal except as a Squire/Acolyte. I'll take further argument to the gameplay board.