Stan, my understanding is that it does eat away at all the steel. The original cutting edge become smoother and wider as the rasp or file wears. I don't believe an acid bath can do a controlled sharpening, but I think there's more surface area on the bevels, for the acid to attack, than on the dull edge. So, somewhat of a point starts to reform, as well as an overall rougher texture.
I believe the important part is that it has to be a quality high carbon steel file that is through hardened, so that any steel that's uncovered is also hardened. The thing that I've noticed is that sometimes there're a few random coarser teeth that leave scratches that the same file might have done a bit better job at if new. I suspect it's less of a thought if the tool is intended for wood work. Just opinion, that's all.
