GC is a constraint filter which controls the maximum saturation differential allowed in a render.  It can have the effect of rendering a sharply lit scene more bland.  It can also bring out details which were too dark to perceive in the uncorrected render.  If one is going for a daylight look, GC will probably help.  If one is attempting a darkish, noir effect, then it will more likely detract from the desired atmosphere.

Personally, I never use it.  Despite the fact that I "have to".

Klebnor

Lotus 123 ~ S-Render ~ OS/2 WARP ~ IBM 8088 / 4.77 Mhz ~ Hercules Ultima graphics, Hitachi 10 MB HDD, 64K RAM, 12 in diagonal CRT Monitor (16 colors / 60 Hz refresh rate), 240 Watt PS, Dual 1.44 MB Floppies, 2 button mouse input device.  Beige horizontal case.  I don't display my unit.