When you have a gaing party and there is a 2 coop available, 3 or 4 guys can take turns and have a lot of fun watching the other guys play, when they're not playing themselves. They can also use their off-time to eat some snacks. :P
the pre-ordered on ps4 specified that there is 1-4 player and 2-32 player server so my guess there is going to be bigger pvp game mode other than 4vs4 and probably 16vs16...if its true that's going to be awesome and insane!!!