I have simple question. Simple?

My guess:  If it's a large enough area, it will show a number of things.  I've cut a square of one inch thick steel, when the head was not straightened correctly.  Examining the cut surface showed taper in the cut, like the whole piece was skewed in one direction from top to bottom.  Without a careful examination like that, I would have cut a whole batch of bad pieces.
Also, if your cut surface starts to get wobbly/bumpy (strafing?) it means that either your mixing tube or your orifice is going bad, or else you're cutting your material too fast, or you have a minor malfunction in your garnet delivery.
Also it just looks really cool, like the inside of a fossil or something.