The reason you see people train to "sweep" left/right is for two main reasons; First, it helps break up tunnel vision caused by "Wacky Tacky" ( tachia psychia or something like that, ha) and Second, to see if there are "multiple threats" as the fight could be over or just getting started! One should also look over their shoulder, while still being aware of where their muzzle is pointing. "Finger off the trigger until the sights are on the target" keeps one from shooting what they don't want shot. Train as you fight, fight as you train.