This is a serious problem even in Friendly Fire-Off games...makes healing difficult and shots get blocked frequently...
Kinda ironic too, because in even in Counterstrike, you're more accurate when you fire standing still...it's only in Unreal Tournament and the like that you really benefit from shooting while sidestepping...
Yeah, there is really no need to move around unless you're avoiding something that's getting close to you (like a fleshpound). The enemies don't shoot. I've seen people constantly sidestepping back and forth for no damn reason when nothing's even close to them, or even worse running in front of everyone to block a doorway so no one else can shoot things (I'm not talking about berzerkers or something--I've seen sharpshooters do this).
If you and your group are shooting at an advancing horde , there is no reason to sidestep and dance around. Stay still, crouch, and hold your ground--especially if friendly fire is on.
Even if something big and nasty is after you, try to be consistent, move in a straight line, and stay out of your teammates' fields of fire. The specimens don't shoot, so you're not dodging anything by dancing around like an idiot. For example, if you're running down a hallway to get away from something, stick to one side of the hall so people can shoot around you.