Saving playlists assumes that you can actually find them again. I use one playlist per artist/composer, organized in per-genre folders, and it's a pain to maintain. First, because I end up with a ton of playlists, and secondly because I have to manually alphabetize their order. If I don't order them alphabetically I can't find them, since Spotify has no playlist search/filter. (For some reason the search box autocompletes other people's published playlists, but not your own.)

I agree with the parent, Spotify's playlist-oriented design is a major UI problem.