In VN, the shotgun was sometimes carried by the platoon SGT or similar rank. Logic was if it got to the point where this individual(headquarters group) needed a gun, it was going to be close. I've had a lot of hunting experience with a shotgun and feel I'm quicker and more lethal with that than with the AR. In a "need for speed" scenario, I feel I can fire and transition through various targets faster with a pump shotgun than I can aim and fire the rifle. This doesn't exactly offset the situation in which you just spray the room with full auto but the targets I aim at WILL be more likely disabled than those exposed to a random fullauto burst.
I've used a shotgun in a couple of civilian confrontations w/o a shot being fired, fortunately. While these were far different from military combat, the intimidation factor played a big role in the peaceful resolution of the situation. Don't count of that during a serious FTF with a badguy, but, it did work fine for me.