Many of my motivations for 5 boxing have already been stated but playing with 5 characters reminds me of some of the older RPG's where you make up a party of 5 people and adventure around. As some of the others, I do get upset with some of the idiots that randomly run off...

Or the one where I am about to pull a boss and an add walks along and I decide to kill the ad first...but stupid Bllokra pulls the Boss!!! I use damage meters to see which of those loosers was slacking. It's a completely different game...