Why not both options? 

Ideas what that means:

By promoting a follower to a friend you get notified when a friends posts a note. That would help to stay closer connected, like real friends.

Or maybe friends are just defined automatically by profiles you follow and they actually follow back.
If you could filter out notes from profiles not following you back you could focus your attention on friends only. That might help to have more replies and deeper conversations, like with real friends.