Don't know about others, but the shot gun is not for me.
In the military application I'd rather have the M16 or a pistol for times the rifle wont work.
In LE, I've tried them. Every time I picked up a shotgun for building searches or what ever, it always ended up being in the way. Besides if its in range of the shot gun I can hit it with my service revolve, if its out of range of the shotgun, I'm better off with the revolver.
I like the ability to use one hand, saving the other for flashlights, mirrors or arrestees. I can always, with one hand put my revolver back in my secured holster. If you end up with a situation where shooting isn't justified but still might have to wrestle around with a bandit, a shotgun is more trouble then they're work.
There may be a use for others, but not for me based on my time as a combat infantryman or 20 years as a street cop.
I'll leave my shotgun for bird hunting or clay pigions.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071