i read once that in actual LE firefights, (memory not as good as it once was) that cops and bad guys using handguns, hit each other about equal and maybe the bad guys hit more. when the cop had a shotgun and the bad guys had handguns, the cop never got hit. like it's some kind of virtual shield almost. break out a shotty and folks start to scrambling.
my take on this: having a shotgun = very valuable. letting the bad guy know you have a shotgun = pricless.