When learning classical music theory I sometimes have these exercises where I have to write my own melodies after a beginning phrase is given to you. There are tonnes of rules I have to follow if I want to get good marks in it.
For the other theory nerds on here... I need to make sure the first half of the melody ends on an imperfect cadence and the final half on a perfect cadence. I need to make sure that every time I use a leading note, it's followed by the tonic. I can't add accented notes in quiet sections. If the tempo is fast, I should use eighth/sixteenth notes; if it's slow then I should use half notes and fourth notes. I can't make notes outside the given key. No augmented note intervals. The list goes on...
I feel like all these rules really limit me as a composer and makes it feel like I'm getting marks for following rules rather than for writing a coherent, enjoyable melody. This kind of stuff DOES limit creativity, even if so many other things in music theory have helped me in my music.
However, the principle of music theory (or any art form in that matter) is that you should first learn the rules and then you can break them. Just because you learn music theory doesn't mean you're suddenly bound to the rules that come with it. The rules I mentioned were only abided to in very early eras like the Baroque era anyway, and I'm only following them for marks. I can use their principles in my music if I want, but I'm not forced to.
Then there are tonnes of other things in music theory that truly have helped me and will help anyone else, like modes, chord progressions, cadences, etc. I would have never thought of making a song in the Phrygian scale, which is basically C major starting and ending on E (and of course any transpositions of it). Even if I did think of it, I wouldn't have thought of shifting the third note of the scale up a semitone for the Jewish scale. These two scales sound awesome and work fantastically for world/ethnic music.
So yeah, like many other people in this thread, my point is that music theory will do nothing but help you, so don't worry, it won't bite.