If I played live poker, I might occationally show a bluff, if I thought, it could tilt the opponent. But other than that you are just giving away free information. I am on online player, and it happen quite regularly, that people show their cards, when everybody fold. And its nice of them to do that, but also a bit naive to be honest.
For instance in a recent MTT I was facing a very large open raise to at least 4BB, when I was in the big blind. I thought, this looked really strong, so I folded a hand, I would normally defend with. The opponent then showed AA, and I was like "ok nice hand and thanks for letting me know, my read was correct". In another recent instance I folded KQs to a 3-bet, and the opponent then showed AKs, once again confirming to me, that I made a good laydown.
I guess, people do that, because they are proud of their hands. But if your goal is to win, then this is not something, you want to be doing. Instead you want to keep people guessing, so that maybe another time you get called by worse.