Steam Internet Session vs. Lobby Session

I was hoping someone could enlighten me on the different session types for Steam subsystem (expanding into how other online subsystems use these would also be bonus)

  1. When changing the bIsPresence flag the Steam subsystem will either create an internet session or a lobby session. What is the difference and when should I use one or the other?

  2. When setting the session name to either GameSession or PartySession, what is this doing? It seems like the same thing bIsPresence is doing.

  3. When using different session names (GameSession and PartySession) it appears I can create both a party session and a game session at the same time with Steam, but I do not think this is the case. Example: If I create a GameSession, and then try to create another GameSession it fails because it already exists, but if I game a GameSession, then a PartySession, then ANOTHER GameSession it succeeds. Does this mean the original GameSession is destroyed automatically?

I’m also interested in this question. Hopefully there will be a answer sooner.