As an end in itself, it might exist to give employment, or an interesting hobby, to someone who loves music too much to leave it alone, much less to have to find another gig.
When there is a rule book, there is a practice period which that 'book' explains, eg., Baroque, Mannheim School, late Romantic chromatic style, serialism. If you are trying to get it right in terms of these schools, especially if you have to be graded by a professor, you have to know this stuff. If you are trying to make music qua music, maybe not so much.
Here's an interesting anecdote:
"Zappa... bought a copy of H.A. Clarke's Counterpoint: Strict and Free (1928), the second page of which began: 'Never write any of the following successions...', then gave musical examples with explanations. 'Numbers 1 and 2 are very harsh...' The intervals were F and A, a major third, expanding to E and B, a perfect fifth. Clarke... said you could not write [...], a major third, expanding to [...] a perfect fifth. Frank played them on the piano.
He never read any further."Frank Zappa wrote:Why? Why can't we do this? This sounds great!
Now, mainly because I thought, eg., J.S. Bach and F. Chopin sounded 'pretty good', I went much further than this basic sort of theory text. That isn't to say my thing sounds better than FZ's, by any means.
I hope this is useful to someone, and not strictly-from-argumentative.
