WTF is so special about Spotify anyway?!

So I kept hearing Spotify spotify spotify is so great.

Brother sent me an invite so I signed up under an alias...I don't 'get' it.

I went to listen to a song and it was like, oh you can't have that unless you pay for a premium account, but you can upload the song if you have it.

WTF?

If I have the track already (& I actually do it was just a 'test' to see what would happen when searching for the song) , why would I wast my time & bandwidth uploading it to a service that supposedly is all about GIVING me music.

I know I must be missing something fundamental about how this service works, otherwise, it's just another retarded on line trend like Fakebook.

So, some of you here must be Spotify users.....am I missing out on something that should be obvious or is it just so much more Bullshit / much ado about nothing?