When hosting a game, one often wants to play only with some buddies, not with anyone who joins.
But since everyone is assigned automatically to an unused playerslot, unwanted players will be disappointed or get the wrong impression if they become unassigned if the host was briefly afk and didn't unassign immediately.
With D209 players can select buddies in the lobby list. This feature can be used to add a new option that changes the mechanism to only assign joining players to unused slots if they are buddies.
This way some of these discussions are prevented and a lot of configuration work for the controller can be saved.