Two more quick points about constraints:
1) In using Galen H. Brown's quote for my own purposes, I should at least have gone on to add his next statement:
The question then becomes “is it ethical to deviate from your personal aesthetic preferences in order to appeal to a larger segment of the public,” and that question has nothing to do with “taking advantage” of anybody’s “ignorance.” My answer to that question is that it’s a personal choice.
I want to be clear that in arguing for the appreciation of a constraint such as the need to communicate with an audience, I don't mean an artist should sacrifice "personal aesthetic preferences." What's fascinating about trying to communicate with an audience is finding a way to do that without pandering: one's own "aesthetic preferences" become yet another constraint to be reconciled with the desire to have an audience get the message.
2) I mentioned here that the idea of improvisation and making something good out of a "mistake" has life applications as well. The same is true of the "constraints" principle. Christian doctrine teaches us that living according to the discipline and limits of God's law is actually freeing and makes us more fully what God wants us to be. In fact, pretty much any moral code is based on the idea that adhering to constraints is good for us. Again, I don't mean to suggest that every possible creative constraint is good and that the absence of them is always bad. The most important point is that we tend to undervalue them; for example, the modern aesthetic tends to see rhyme and meter more as crutches for the uncreative rather than as tools of inspiration. For better or for worse, the fact that we have a much less established set of creative constraints in our age makes it more of a challenge for audiences to understand context.
I wrote here that I think the 16yr-old Mendelssohn's Octet may be as perfect as anything ever created by one so young; that's possible in part because he had the advantage of writing within such a well-established system of rules for tonality, counterpoint, form, etc. That's not to take anything away from his achievement, but though I can imagine a young composer today might create something as magnificent, it's hard to imagine that it could seem so perfect. There's not a clear enough context in which to make such a judgment. No, perfection isn't the only goal to which art should aspire as I've suggested here. But I'm glad we have that Octet.