the element of surprise is what you want.
if 2 dudes enter a place intent on robbing it, your open carry ass is going to be the first headshot before they announce anything.
Better to be just another scared face in the crowd they're controlling - at some point BG #1 will be close with back turned. You pop him in the head, and while his buddy is looking for the source of shot, you're putting 5 in his torso while moving against his body - covering your brain with cupped hand and heart with elbow.
move, shoot, live.