You show bluffs to get loose calls, when the table isn't otherwise offering them. You do it to make your opponents play worse, if their play is not already bad enough to make you a good profit. What you're doing is mimicking a bad player, a maniac, a loose fish. You're wolf in sheeps clothing basically.

A better option is to find a better table, but there's nothing like milking a bad image for all it's worth by hitting a hot run of cards after bluffing a couple times. It's priceless.

I show a lot of bluffs. Most of the time because I'm in the mood to screw with people. It's fun. Try it sometime. Just be careful not to do it one too many times. It's definately an art form. You need to do it on the right boards, following the right lines etc etc. Not super easy.