This buffer determines which parts in render are seen by the viewer and will take out the parts that are not. Leave this option enabled. Only disable optimization if you have weird anomalies in your games. Anti-Aliasing is what everyone is talking about. It takes out jaggies and sparklies from your image.
Jaggies are staircase-like formations on edges of objects on screen, particularly diagnols.
And sparkles come from poorly aligned texture seams. Best for compability. Totally recommended if you want speed above all else. Don t even bother playing FPS games with these, you ll be the one who is fragged instead of fragging. This option is great for other slow-paced games.