[kin]

I think the library is probably the biggest thing for OP. I mean, when I first tried using Spotify and found out they only had a single track from Blink-182, I immediately stopped using it. They have their entire catalog now, but, I'd imagine still not some songs for OP which, if a service doesn't have an artist/song you want to listen to, why use it?

[barkingtoad]

If you own the music, you can add it, and it is then available to you inside Spotify.