Music theory is totally useful! let's take another example: Knowing what a compressor does it absolutely helps to know what ratio's, attack, make-up gain and so on do.
BUT and this holds true for all theory, the final decision needs to be made with the ears/heart/soul/intuition, and breaking the rules is fun.
The good thing about not knowing stuff is that you're then the wide eyed child, messing around alertly listening to what happens. I have noticed all the really good engineers I have worked with tend to have this attitude, not make assumptions, just try out stuff and see what works. I call this "beginner's mind".
