Values listed in brackets are for alternate (secondary) fire.
The shotgun is the basic weapon for the support specialist. Like other shotguns, the pellets penetrate multiple enemies, making it perfect for dealing with groups of enemies. In addition, its raw power makes it useful in taking down the big guys. Its total un-perked power output is 35 * 7 = 245 damage per shot.
It is one of the three weapons that has a flashlight, the others being the 9mm and the combat shotgun.
As with any shotgun, it is important that you reload as often as possible. Reloading fully takes several seconds, which in a tight situation may lead to your untimely demise.
Try to avoid using over long ranges, since the spread makes it ineffectual at anything beyond medium range. Getting head shots with the 9mm will likely do more damage than a single pellet.