V-Sync, what is it exactly?

[DoubleJG]

Just wondering what it does when it's turned on. Someone said by turning it off you get less slowdown, yet if it's true, what do you lose in return?

[uhawww]

V-Sync forces frames out from the graphics card to 'sync' with your monitor's refresh rate. This allows for complete frame display, but throttling the graphics can slow some machines down.

Running without v-sync can speed it up, but your graphics adapter will push out frames as they render, independent of the monitor's refresh rate, causing the frames to display at once. When there's a lot of graphical movement, you will see a thin, nearly invisible translucent horizontal line where the frame ended it's render, and it will warp or slide around, based on the asynchronization of your gfx card and monitor. This is a bother to some, ignorable to others...

[DoubleJG]

Thank you.