It's just a framework. Like music history, ethnomusicology, music cognition, music lessons, instrument building, etc., it will deepen one's appreciation for music if you learn it.
As far as composition-- I've had some encounters with talented musicians who get stuck putting together a song or electronic composition because "something just isn't sounding right." In those encounters, a process of elimination improved a chord/voicing that an understanding of fundamental music theory principles would have revealed without my help.
The problem is that without the fundamental understanding, it's nearly impossible to reverse-engineer such an improvement and deduce the general principle at work. Lacking that basic understanding makes one reliant on others just to figure out how to get the sounds out of one's head and into the air.
