The Crossbow is an Average-condition special weapon for silent kills. It reloads slowly, but bolts make no noise. It gets more useful as you unlock more bolt recipes.
Use it to clear Marauder camps and Infestation zones without alerting the area. It is ideal for sniper towers and lone guards. Once a fight goes loud, switch to a gun.
The Drifter Crossbow is the Military Spec upgrade and fires more special bolt types. Move to it when you can. The Rock Chuck also kills quietly, with a built-in suppressor and a 35-round magazine.