What Does V Sync Do. All it does is to impose a framerate cap, limiting the maximum FPS to the equivalent of the monitor's refresh rate. To start, let's look at how graphics are processed in your computer.
Did you ever felt that the game is not as responsive as it should be despite having a good RAM and CPU capacity? This has the positive side effect of limiting the amount of frames per second the computer has to draw to the monitor refresh rate. Vsync does introduce a few issues of its own, however, as a result of the way it throttles performance.
Does it block when you clear the screen or when you flip the buffers? vsync blocks front-back buffer swapping until next display sync signal.
If you're viewing little amounts and it's not an issue, then don't bother with Vsync.
It is usually either on or off. V-Sync has a single purpose: eliminating screen tearing. Vsync makes the graphics adapter wait for the monitor to signal it's ready for the next frame to ensure all displayed frames are always fully drawn.