Peter's right about the creative musical process involves working with rules and around them and inside them; but Charlie Parker is right about music having no ultimate boundaries.

There's an infinite set of types of music, and to be on of those types there are rules; if it's a waltz, it's got to be 3/4, no arguments. So if you change around a waltz so that it isn't 3/4, it's some other type of music. And maybe it's a type of music that hasn't been in existence before, and the imaginary boundaries of music generally has been extended.

No different from poetry - if it's a sonnet it's got to have one set of rhymes, if it doesn't it's not a sonnet, but that doesn't stop it being poetry. And the same when you abandon rhynme, or abandon metre, it's can still be poetry.

Most of the time I seem to prefer to work within a set of rules, and prefer artists who do the same, but that's personal preference rather than a macro-rule..