This is a critical weapon to carry, so make room in your inventory for it if at all possible. It's perfect for that occasional situation where you get swamped with guards because you've tripped an alarm, or if you know that a guard is about to walk through a doorway. You only need one melee weapon, so open crates with your knife. Grenades also stack in your inventory, which is a nice space-saving side benefit. Grenades can be attached to walls to explode upon detecting motion, which is a good way to avoid a difficult encounter if you can scout the route of an opponent.
Most guards wear armor that makes normal ammo useless.
Recoil makes it impossible to aim a burst unless you're an expert. Some nonplayer characters will be impressed if you are less violent, but nonlethal methods are much less effective. Don't bother with them. Embrace your dark side. Last Words Deus Ex should be played as a stealthy first-person shooter, with exploration and gathering information as its keys.