I'm sorry if this is a dumb question, but I've dug around a bit and I'm still not totally clear on this.
My understanding is that you can only save 10,000 songs to your library, but you can add an unlimited number of songs to playlists. Is that correct?
If so, what's the difference between saving a song to your library versus adding a song to a playlist? Put another way, what does saving a song to your library allow you to do that adding that song to a playlist doesn't allow you to do?