The throwing knife has the distinction of possessing the longest range of any thrown weapon; however, it does not deal a significant amount of damage.
Its usefulness is disputed due to the low damage, but it has the ability to knock enemies unconscious on a critical hit, rendering them out of the way for many turns. In this way, the throwing knife is essentially an instant kill - you can knock them out, then hit them in the eyes with 95% hit chance to kill them very quickly.