synchronisng a framerate that is higher than 60 introduces a delay period of approximately 20ms (where a framecapped no vsync 60fps is 16ms) This can be felt in most first person shooters with vsync enabled (on 60hz displays atleast).
capping the framerate at just below 60 when using vsync+TB allows the frame to display Just-In-Time, and thus the latency is always 16ms max.
Im sure theres a far more clear way to explain it, but put simply. try running Doom 3 with vsync (mouse smoothing completely off) and you will find it feels like you're dragging the aiming reticle around the screen, where as inputting 57 or 58fps as a frame cap (Nvidia inspector or Dxtory) the input will feel far more responsive.
Homeworld 2 is another title where the frame cap really helps.
Ok just to clear out some fast. |
Basically the problem is that the game engine sends more frames that the monitor can display in a second, for example your Pc can run the game at 100 fps, your monitor can display 60, so while the monitor refreshes it's vertical lines, there will be lines what till display an older frame, some a new frame so the result will be a tearing picture.
If you turn v-sync on, the game will still make 100 frames, but it will go into a buffer, and the buffer will send the right amount (in this case 60) to the monitor to let is display every frame separately, without tearing. The mouse "lag" you get is because the frames have to wait for the monitor so you get a bit of delay.
more info: http://www.tweakguides.com/Graphics_9.html