Both CompizConfig and the Nvidia X Server settings have options to enable Sync to VBlank. By enabling the Benchmark option in Compiz I can see that ticking "enable sync to vblank" under General in Compiz will keep the Frames to 30 per second. Unticked, it is about 60. However, choosing the equivalent option in the OpenGL tab of Nvidia X settings doesn't seem to have any effect. Which option(s) should I enable?
It appears that when you are using Compiz, Nvidia X Server settings' Vblank option does not work. If you are using Compiz then select the sync to VBlank in the Compiz Settings. Otherwise use Nvidia's setting. VBlank is useful for watching videos and playing games if you experience "screen tearing" which is horizontal lines occasionally distorting your video. Enabling Sync to VBlank will usually fix the screen tearing issues.