Obviously I don't know about everyone else, but. . . .
As I cut more I started to get a better understanding of what the final result would look like. In my case I tended to cut things too deep, especially lettering. It looked a lot better in a preview but the execution can be a pain not to mention if it is going to be painted.
One of the issues with "carving" on a cnc is shadow lines. I have written about this before but I will repeat it (that is what old guys do, repeat themselves). The issue is that a cnc machine when doing 3D work that requires a ball nose bit does not produce a sharp shadow line. When we look at a carving what we see are shadows and shadow lines, that is what tells us about depth. That rounding by the ball nose causes what should be a sharp shadow line to be muddled up a bit and the result is it never quite looks right. Of course that is also dependent on the intended viewing distance vs the radius of the ball nose cutter. Things that are to be viewed from far away need to be cut deeper.
Myself? I have no problem picking up a gouge and sharpening things up. My thought is that the idea is not "oh, look, my cnc did this completely! Isn't that great?" It is more like "I created this and I want it to look right and if that takes using a few more tools, so be it."
As you do more things you will start to get a better feel for how deep you need to cut vs the size and viewing distance of the project.
A good example is a skrat carving I have in the shop. It is not very large, skrat is all of about 3.5 tall. (Skrat for those who do not know is the crazy prehistoric squirrel the Ice Age movies). It is not very large but it is cut very deep, about 1 inch overall. He is typically viewed from about 4-14 feet in distance. With that depth his shadow lines allow him to be seen easily from 14 feet away even though he is small.
The other thing that can really help with a wood carving that is not painted is glazing. The darker glaze helps with the shadow lines a lot.
I am sure a lot of the other folks will wander by and share some of their techniques and observations.
"If you see a good fight, get in it." Dr. Vernon Jones