V-Sync, or Vertical Sync, limits your Frames Per Second (FPS) to your monitors current refresh rate. When Vertical Sync is turned off there is no limit on your FPS, but if your computer generates more frames than what your monitors hertz are set to, you get screen tearing (those irritating horizontal lines). I always turn on V-Sync when playing SHIII, the game feels more smoother and no screen tearing
