A really rough analogy is a programming language. The rules of the language don't tell you what kind of program to write, but choosing a language gives you a huge jump start on creating interesting and useful programs. Likewise knowing algorithms and good patterns.

I think that very few people are interested in studying music theory as an end unto itself. Like, I have a friend who is a retired theory professor, and did his PhD in theory. (He also performs music, but treats it as a hobby). For everybody else, the purpose of learning theory is to make you a better musician. So you can take it as far as needed to make that happen within its applicability to the kind of music you're interested in.

And there are different approaches, such as "jazz theory," that doesn't spend a lot of time with (for instance) the forms of larger musical compositions, or Bach.

So, what aspect of your musicianship are you trying to improve? I can cite one example. I play mostly jazz. I'm not great at theory myself. Everybody I know who can compose good jazz, or create written arrangements for larger ensembles, studied theory in college. I'm stuck with playing their music, which I love, but am not capable of creating my own. The theory probably helps in terms of letting you go from a composition that "almost" works but has awkward bits, and make it really sparkle.