Supposedly it sharpens the blade(s), similar to the oldschool way of using a piece of leather to accomplish the same thing. Move the blade up the underside of your forearm (where there's no hair), in the opposite direction of how you would normally shave.

IDK if it actually works but it makes me feel better.

Probably best hunt up a video. Know how you strop a blade against a strip of leather? Same deal, but with the underside of a soapy forearm. Push the blade backwards against the tensed muscle. It really, really stretches out the useful life of a safety or plastic razor. Caveat: If you do this a lot the underside of that forearm will lose some hair, even though you're pushing backwards.

My hair isn't tough or thick, and my Asian wife is all but hairless, so we can use the same plastic razor for months. YMMV.