wakelagger

Disabling vsync will let the videocard output fames to the monitor as fast as it can make them.
Enabling vsync will slow down the video card so it will output frames at the same rate at which the monitor refreshes, or draws a new visible frame.
Disabling vsync has its disadvantages. Most noticeably on first person shooters where quick rotations and fast action are the norm, 'tearing' of the frame will occur. Basically, if you are moving in a straight line without vsync on, then turn quickly, this is what may happen.
The videocard sends frame 1 to the monitor
The monitor begins to draw frame 1
Suddenly, you turn left to challenge the dastardly villain
Meanwhile, the videocard sends frame 2 to the monitor, which shows your sudden change in direction.
Before the monitor is finished drawing Frame 1, it receives the new and improved frame 2, and it begins to draw the frame before its finished with the first frame. This results in a tear, which I will attempt to demonstrate with the wonders of ASCII art.

Vsync On
Frame1 Frame 2
******** ^^^^^^
******** ^^^^^^
******** ^^^^^^
******** ^^^^^^
Vsync Off
1 frame for monitor, frame 1+2 for video card
********
********
***^^^^
^^^^^^


If the tech guru's of the TFP concur with my 'art' and explanation, huzzah me.
If not, attach, me to your standard +5V stand by line

edited for lining up the ASCII 'art'