To Show Or Not To Show

I have heard some people say you should never show your cards. Showing them they say is giving them information, and as poker is a game of incomplete information any little info garnered is an advantage to your opponent.

Where do people lean here on whether to show their cards? I have seen people show their cards after a bluff, is that a good thing, it rattles me thats for sure, annoys me and psychologically gives them an edge on me

Trev