It really isn’t that much, if you like having the option of listening to every album you like by a band you like, i.e. having a Radiohead playlist with every Radiohead album, including B-Sides… that’s about 150 tracks, which is about 1/20th of the limit, and there are actually quite a few other bands like that, it all adds up quickly even for bands that don’t have that many tracks I like.
I used to just have my favourite songs downloaded by bands I like, but eventually you get bored with what you’ve got. Inevitably you’re going to want to add more.
I probably don’t need that many tracks but it’s still nice to be able to listen to all your shit when/wherever you want, esp if you’re travelling and there’s no wifi, (even then the wifi’s usually shit anyway). Even though there might be downloaded tracks I don’t listen to much now, I might want to listen to them at some point in the future, without having to constantly delete/undownload stuff to make space and then add it again.