So I spent a couple hours in the Ringed City with my summon sign down in the second bonfire. I was summoned as the boss twice, which is a break for the player because as the summoned I get no estus and I just don’t have the patience (or ability) to win that kind of fight.
I also got summoned for Midir several times. In probably 8 trips to fight Midir the best I have done was me and the guy who summoned me once got Midir down to about 20% health.
But the fun stuff is getting summoned to help a player get from bonfire 2 to bonfire 3. I have done that several times in the last couple days and have been involved in some massive PvP play. Invaders love to invade in that area, and you add in the regular enemies and it gets pretty crazy. I once picked up almost 300k souls from one summon. I can only think it was a not too high NG+ host.
I ran into a very high NG+ Pontiff summons the other day. I don’t think I have ever been hit that hard by any enemy before.