I tried searching here and elsewhere on the web but was surprised not to find any information. Please direct me to a link if I've missed something. I've often wondered about this because I've heard from certain DPs they prefer 0db to -3, although I was skeptical.
I usually default to -3 when possible shooting for less noisy shadows. Mostly oblivious to the pixel peeping consequences that may happen otherwise (I never outright noticed anything)
Recently on a shoot with some deep purple fabric and I noticed switching between -3 and 0 completely changed the purple to a completely different color. The settings in the low and mid areas matched and I couldn't figure out what was causing that.
Check out your low, mid, high settings in the paint menu, The switch on the camera that changes gain also changes a lot of paint menu functions. I've found that some of the scene files floating around don't have consistent settings (especially for matrix and color correction menus) so when you go from low to mid you may be turning off color correction in addition boosting gain.