It won't hurt the card nor the monitor. If you enable Vsync, the refresh rate of your monitor will be the limit. With Vsync disabled you can check the power of your Graphics card, but your screen won't actually draw the entire picture according the FPS. That means that what you see isn't actually there! The picture will be only partially synchronized, some parts of the image being older than others. In the worst scenario the guy you're hunting would in reality be already in your six! And who'd be the one to blame? Not him, he wouldn't have done anything wrong although from your point of you he'd been warping. Yepp, for gaming it'd be wise to have Vsync enabled.
