I'd say they were created to enable or do that, but that's not what they actually do. Remember that the crest is actually composed of Magic Circuits, which may or may not actually have spells 'loaded' into them. One of the problems that seems to face modern Mages is the sacristy of Magic Circuits, you only get what your born with and what, if any, you inherit via a Crest, and apparently those you develop naturally isn't normally that many, at least by the standards of things you may want to do.
And one thing I read suggests that Crest Magic Circuits 'loaded' with a spell are useless for anything else