How useful are musical categorizations?

This is a question that I find myself asking periodically, and the other night I found the impetus to write about this. While watching a little TV, I see a commercial for the new Helmet album. First, I had no idea Helmet was still around, much less making a new album. More importantly, however, is how it was marketed (and that will be the crux, I think). This testosterone-driven, aggressive man's voice said, "Helmet - the prog-metal gods!" I immediately (and half-jokingly, but only half-jokingly, said, "Prog-metal? Didn't they used to be grunge?"

This leads into a bigger issue. Musical categorizations are so difficult. About four years ago, when asking some teens about what the fuck emo was (besides bands with shitty names and shittier music). To put this in context, Weezer had just made their "comeback," with 2 albums in less than a year, and I found them rather underwhelming, compared to the so-called Blue album and Pinkerton. Anyhow, asking what the fuck emo was, they couldn't explain, so they tried to name bands, saying, "Weezer's emo, and Dashboard Confessional, and At the Drive-In." I was immediately furious, because A) I HATE retroactive labeling of bands. Given there WAS NO emo in 1994, I failed to see how Weezer, who, if they had changed their sound, had simply dumbed it down, was suddenly "emo" in 2001/2002, and second, besides the fact that Weezer, Dashboard Confessional, and At the Drive-In all make music, there is NO similarity. It's like saying that Ellington, Django Reinhardt, and Wayne Horvitz (more on him in a second) are all jazz. All of this just left me wondering, in an earlier time of life, if labeling types of music into specific genres was useful for anything more than marketing ("Buy the new Weezer album!! An emo-masterpiece!!!!")

Finally, there's the aforementioned Wayne Horvitz. A friend and I had the opportunity to see him play a few months ago, and while it may have been jazz in the loosest sense, both this friend and I were discussing how many boundaries it crossed, how you can't really classify it (a point, we soon learned, that Horvitz himself made in the liner-notes of the new album). Again, was saying something was "jazz" or "free jazz" when really it incorporated jazz, blues, and classical in new and fascinating ways useful for anything besides marketing?

I'm still very ambivalent about genre-labels. In the most general sense, I guess they can be useful - if you're trying to explain to somebody what Joe McPhee is, "jazz" is more appropriate than "blues" or certainly than our general understanding of "blues" or "classical". Nonetheless, beyond the most elementary level, I'm really not sure that genre-labels have much to offer in understanding music. What's Sonic Youth? They have elements of "No Wave," "punk," "jazz," "ambient," and numerous other styles - "Alternative" might be useful for the most basic, "what kind of music does Sonic Youth play?" question, but it doesn't answer anything.

Anyhow, if you in the so-called "blogosphere" have any comments, I would love to hear them. I'm definitely unsure if and how labels, or even words, can accurately describe music.