There is a Music Theory group on Facebook that I enjoy following. The members are a mix of folks who know something about the subject and others who have no idea at all and are trying to find out. Someone asked how knowledge of theory will enable someone to, for instance, perform a Beethoven Sonata better. My answer –
Way back when, what made me switch majors from piano to music theory, was seeing my great piano teacher mark up my scores with pencil, so much so that you could barely see the underlying score. The score meant something to him that I couldn’t see on my own, and as I didn’t want to need someone to interpret the score for me, but wanted to get it myself, I switched to theory – and never looked back. You simply cannot understand the composer’s intentions without knowing what he or she knew about musical structure, harmony, counterpoint, etc. Your ear will only take you so far. It has to be supported by knowledge.