I've been thinking about paintball recently, one of my favorite activities, and I've come to the realization that in paintball you kinda have to be facing the cover you're behind. If you put your back to it, you really can't see what's around the corner without poking your entire head out slowly, and firing from that position is basically impossible.
So I've been thinking, why do characters in games always put their backs up against cover? It doesn't seem like a smart thing to do. Facing the cover allows you to pop up quickly to see what you're facing.