Depends on setting and the level of realism involved whether or not guns are appropriate, prolific, and powerful. My own post apocalypse setting for instance has lots of guns and ammo. On the flip side, its set in the near future with creatures and characters that can eat several bullets and remain standing. Ergo, guns are appropriate, setting was made with them in mind.

Versus, say, the extremely stereotypical zombie horde post apocalypse. Having lots of guns and ammo there defeats the fear of facing a horde of zombies. Now if all you had was a hand gun with a halfway depleted clip, that makes lots of noise, and a crowbar, and you + you buddies had to slip through an apartment with a couple hundred of the fuckers... Well... Suddenly it becomes a choice mechanic: Save your friend but attract the horde, or leave him to die as bait for the horde so you and the rest can escape.

Guns are always dependent on setting.