"When I play CQB I love playing with my shotgun. I haven't seen other players using one, but that may change! For me, this is more fun than playing with an AEG, and it does generate a lot of conversation.
The advantage of a shot gun is that if you are doing snap-shooting, you have an advantage because of the shotgun spread. Also, it is much lighter than an AEG so you can maneuver around and it is easy to fire with one hand similar to a pistol.
Another advantage is the range. Every time I play I have someone come up to me and say they are amazed that I was able to shoot them from across the building. Mentally, people are not prepared for a shot gun that matches the range of their rifle.
The disadvantage is that you don't have the ROF of an AEG. Some people like to stand off and fire across the room and try to pin people down. You can't do that with a shot gun. And you also have to be strong enough to pump it, I am an adult and I have no problem pumping it. Also, replacing shot gun shells does take time if you are used to hi-cap magazines.
Even though it does not affect the actual play, I also have to say there I get a sense of satisfaction of the sound of pumping the shotgun. As we get ready to play, it really plays on the nerves of the other team when I pump it."