[Zweihander]

They're useful on a personal level but not on a broader level.

When you want to listen to some Drum & Bass, you already have a personal classification of the music style and artists that you're looking for. It's going to be different from someone getting into that genre right now but if you wanted to listen to what they wanted to listen to, I'm guessing you already have some personal term for it (Nu, progressive, modern vs classic, ect.).

When talking to other people and using music services, that all breaks down and you usually start going by similar artists or meaningful tags. Similar artists is an inefficient way to classify your music (both in your mind and in your folders) and meaningful tags works but requires significant effort to actually keep them 'correct' (and if they're not correct and just for personal use, you might as well use genre's).