jokekid wrote:so Vsync actually enhances performance?
Depends on how you look at it. It limits the speed the game is continuously running at, so performance of the game is more stable except on very resource intensive moments where the fps drops below the current vsync fps. So the game itself is actually running worse, but it keeps unneeded resources free. If vsync limits from 100 FPS to 60FPS (and assuming each frame takes the same amount of time and resources to compute), you've decreased process processor usage by 40%. It's got some downsides but most of those aren't technical. But this is the basic gist.
This one is a bit more detailed: http://hardforum.com/showthread.php?t=928593