Curves, dimensions, layout,planning.
Curves sound the best and since I am partial to carving bears , there are lots of curves. A fully fed healthy bear has big gorgeous curves, a bear that needs to bulk up is sinewy but still has muscles that give it curves.
If you think about it, even if you are untrained and an artist or an architect you mostly know when something is out of whack but you might not know why it is out of whack.
The head could be too small for the body, the muscle in the back leg is a little too far back or too far forward.
These all matter for the overall piece. Regardless if the carving is realistic or abstract, curves matter