I think what's more important than knowing how music might follow a predictable pattern, a series, in the theoretical sense, is to have an intuitive knowledge of the instrument that reaches to the subconscious. It does'nt matter what terminology is used, whomever has the best aural skills "wins", so to say.
If you are in a formal ( symphonic, jazz, classical, etc ) scenario where a common standard must be upheld to maintain some sense of order, then music theory is essential to sustain communication between the band members, or to a conductor to his orchestra, so everyone is on the same "page", so to speak. But in an environment involving two or three stringed-instrumentalists, a percussionist and perhaps a vocalist, boundaries dissolve and expression becomes much freer, because no regulation as to how music is conducted is enforced.
But ultimately, everyone abides by some theoretical system when playing music, otherwise they might be a completely abstract thinker, and play music that goes in no direction! Whether you have a degree in music theory or you simply play by ear, hard work is the key. Both methods of learning aim to accomplish one thing : To reproduce on the instrument what you hear in your head, thereby expressing yourself. So then, its simply a matter of preference as to how you learn to do it. Just like some children in school learn much more efficiently by reading something, as opposed to having it orated to them, or as opposed to having it shown to them in images, so is learning how to express yourself with music.