Theory in all endeavors, musical or not, is important only if it derives from the need of one’s essence, rather than being only other people’s ideas or thoughts. A useful theory must blend and bend into one’s own being; theory has to be self-made. Theories which have been formulated by others can certainly assist and are especially helpful if they involve technique.
One must identify one’s aim, and then do what helps that aim. Methods without philosophy are insanity, and philosophies without methods are babble; I realized that when I was 19. I did not feel that traditional music theory allowed me to fulfill my aim, and I had a mission to not allow it to interfere with my own musical approach and identity; hence, I turned down an offer to enter Juilliard. Had I not done so, I never would have developed “The Lydian Chromatic Concept of Tonal Organization,” which does not have “do’s” and “don’ts,” but allows for musical expression using all of equal temperament.
The application of theory to one’s work continues for a lifetime, as one is always climbing toward a higher aim.