It really depends what you're trying to achieve. Music is like language. If you want to write a novel that's different from if you want to visit as a tourist. I

It really depends what you're trying to achieve. Music is like language. If you want to write a novel that's different from if you want to visit as a tourist. If you're interested in Jazz theory, then don't get a textbook on classical theory (Analogy: if you want to learn Portuguese, don't study Spanish instead, even if knowing Spanish will help). If you want to compose original music, you don't need music theory. If you want to compose in a particular style, then study that style and its conventions. If you want to talk with other music theory people, err... why in the hell would you ever want to do that? It will bring you no joy and will take over your life nonetheless.