Originally posted by Complaintdesk:

There is an increased damage modifier while in sneak-mode while a dagger (knife) or bow is equipped. I can 2-shot trolls with my bow while crouched. I have found if I am alert and listening, I can detect most enemies at distance (while travelling not in sneak-mode), whereby I crouch, just before I am detected by them, then attack.

This is not limited to just knives and bows -- it applies to any weapon with "Backstab bonus" in its stats.