These utility node groups are commonly used in CG Cookie video training material, especially material/shader building content. They serve as neatly packaged versions of their underlying complex shader networks & formulas.
CGC_Fresnel: This group is based on Kent's preferred fresnel implementation, for controlling reflection falloff.
CGC_Absorption: Based on Agustin Benavidez's implementation, serving to calculate varying geometric thickness. It's useful for controlling a light absorption effect. Functions with Translucent and Transparent BSDFs.
CGC_Fake-Caustics: A wonderfully useful trick for faking caustic effects without having to wait for the expensive render times of true caustics, based on Bassam Kurdali's implementation.
Intended use is to append these Node Groups out of their Blender scene file and into your Blender scene. So from your scene, go to:
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