Vsync off stops the refresh rate of your monitor restricting your FPS. Basically if you wanna do FPS tests disable Vsync, but if you wanna play enable Vsync as switching it off seems to produce rubber bullet effects and not just in AH either.
Usually with Nvidia cards its best to set all options to maximum as the display improves with minimal if any noticeable decrease in FPS.
Except FSAA of course maxing this out will have dire consequences for most Graphics cards on the market.
