Composite Render Passes in PhotoShop
Basic example with a few Render Passes in PhotoShop
Ambient Occlusion AO pass
Specular Highlight pass
Material ID pass also called Clown pass
Beauty pass
These images are used in PhotoShop for some quick post processing instead of waiting for a rerender.
Change color on specific parts
Tweak the look and feel of the ground shadow
Adjust the amount of specular highlight
add some extra ambient occlusion
add a Glowing effect around lit up parts
Hope it helps :)