To put my cards on the table at the outset: I am against post-work of any kind.

However; with that said, let me qualify. My love of 3D modeling is aimed toward animation...and I want to see the impossible done in the program. I think the perfect comment under an image would be: "I was going to fix this detail in post, but figured out a way to do in the render." Because with a ten second animation @ 24fps, you can't go in and fix something on all 240 frames.

On the other hand: if your interest is a single stand-alone image, then anything goes. For example, I do illustrations in colored pencil. Sometimes, if the colors go wrong, and I need to backtrack, I'll mix a very thin slurry of white oil paint in turpentine and apply as many layers as I need to tone back an area. [The pencils are water soluble so I can't use opaque watercolors.]

Basically, I see the whole issue as two camps with different aims: Illustrators and Animators.