Music Theory is such a broad term. Do you mean the study of 18th century European music? I can say i don’t use basically anything I learned in all my college theory courses - it was all knowledge that had little to do with my listening experience. For example, I would get questions wrong on an exam because I said a certain type of a sound was a 7#11 chord, or a tri-tone sub. When the answer they were looking for was a type of augmented 6th chord. Another example would be figured bass, which i haven’t seen at all since i studied it in college for part of 1 semester. I would say sight singing and playing bach chorales heavily influenced how I hear lines, but I did not memorize them and don’t really reference them unless my task at hand requires it, it’s in my emotional memory.

There are multiple intelligences at play when writing music: Physical, intellectual, and emotional.

Physical is the longest lasting and most accessible: playing on an instrument, vibration responses to the ear (did that sound good or bad), hand movements/shortcuts when using software, basically muscle memory.

Emotional is the most important, as it conveys meaning to sounds. This is what i’m thinking about when improvising at the piano or on my instrument. This combined with trained physical responses is how one “hears” things.

Intellectual is how we translate the emotive quality of sound to english, or also how we can work our way through problems that arise in things like voice leading, part writing/orchestration in general. It’s generally useful to know things like “if i put trumpet on the major 3rd on top of this chord structure, it might not sound very in tune” or “if the intervallic structure of the woodwinds is like that, it’s going to produce this type of timbre/overtone sound”. Sometimes composers use other people to handle the “intellectual” side of their work, i.e. orchestrating and writing parts for a specific ensemble. Most of the time with sheet music however, it appears to be a one man operation.