Definitely helps with stress.
When I'm pissed, I hit the gym. ...and for about an hour or so, EVERYTHING IS RIGHT IN THE WORLD.
Aside from that, being a 100lbs pencilneck growing up wasn't much fun. I get much more respect now, and it's a confidence booster.
When you're tossing a chick around in bed, and they're grabbing your arms and hitting your rock solid chest, things are good!
aX