Originally Posted by Aus_Karlos

Basically this tweak improves the quality of the recommended settings that your computer can run at. It fakes a higher setting with minimal fps loss.
Example if you can run the game in Medium the tweak will improve the image to the point of it looking like high settings.

Also the option r_usePOM requires lots of GPU power. Disabling it will give back aprox 10fps on most systems. All it does is make terrain look more bumpy. Not much image quality loss if disabled.