Most lenses only care about the angular light distribution, essentially averaging over the lens surface. So a ding or crack would just add a tiny portion of grey or black to the entire image
Edit: This is for cracking the front protective glass of a camera lens. If an actual optical lens splits in two it will be misaligned and bad things will happen.
I was already in the middle lf posting this to !dontyouknowwhoiam@lemmy.world before seeing the remainder of your post :)