It's used as a standard way to test how much of am inpact a weld via a given rod can take prior to just snapping in two, you can actually see large enough enough differences between a premium and budget rod of the same spec, eg ER7018, that the difference will show up in an unscientific hammer test.
I find it pretty useful, because a weld seldom ever will break because it was bent and stretched into a full 90 degree or greater bend, but more typically because you ran into a tree with your tractor. Frankly the degree to which a mild steel joint can be bent or outright hammered over is kinda insane by knife standards, most knives won't hammer into a crack free 90 degree bend, ER7018 absolutely will.
