Max Frames to Render Ahead controls the number of frames which are rendered and held in advance of being displayed. The default is 3, however by lowering this setting you may be able to gain a slight performance improvement, you can resolve mouse lag problems, and even prevent graphics freezes in certain games. Experiment by setting this value to 2 first, and then if necessary try an extreme value like 0. However I recommend either 3 or 2 at the lowest.