I found this option in CCSM. It's unchecked by default. There's a tooltip explaining that it allows drawing on fullscreen windows to not be redirected to offscreen pixmaps.
This option causes drawing to occur directly on the screen rather than drawing off-screen and then copying the drawn content back onto the screen.
Thus, yes it can dramatically improve graphical performance.
However there can be a draw-back - on some graphics cards/monitors - using this option can result in dramatic flickering. Particularly - this flickering effect can occur on full-screen apps.
Thus - its work experimenting, but if you see flickering, its best not to use.
Remember using CCSM can break your desktop.
If you want to toggle this value, you can use:
gconftool-2 --set /apps/compizconfig-1/profiles/Default/plugins/composite/screen0/options/unredirect_fullscreen_windows --type bool 0
1 to switch this option back-on.
If you use the Nvidia proprietary drivers, it is very important to unredirect fullscreen windows, otherwise XVideo will not use sync to vblank and you will see tearing while playing videos. The Nvidia driver manual says:
Note that the Xv adaptors will ignore the sync-to-vblank option when drawing into a redirected window.