Theory part of music.

I'm not interested in learning it but I had no choice when I wanted to sing professionally. It's not easy. It is a must if you want to be good at music.

I am very interested in the theory part of music. Problem is I've never had time to take a class (in high school nor in college). I may when all is said and done sign up for one on my own. I don't think it is a must, but it would definitely give people who learn the theory part of music more appreciation in other types of music other than the modern day rock, pop, r&b, rap, etc. You learn why chords are used, why some notes go well with others in certain songs and why those same notes would not work in other songs.

Basically, it's not all that important if you are learning an instrument just for fun or as a hobby. Like a piano for example. You can learn it by ear or if you want to learn it the traditional way is fine. Fir singing, I don't think it's that important. But learning it would help. Like solfege (do re mi fa so etc).