I used to encounter a good-looking guy at Bare Ass Beach along the Great Salt Lake (in Ewetaw) who had a decent 6 inches, but insisted upon pumping. The result was he deformed his cock by creating what, for lack of a better description, were massive water blisters under the skin around the shaft of his cock. It sort of gave the impression his dick was a lot thicker than it was (if you squeezed your eyes to make everything seem fuzzy). Don't know if the condition was permanent, but it definitely appeared to be a dangerous activity. It's too bad, because otherwise the guy was major hot. He just had a bad self image because he didn't think 6 inches were enough. I've never thought about a penis pump because I've got the opposite issue; in my opinion, my dick is far too large. It's always been a problem for me to enjoy fucking women. Never have had the pleasurable sensation of having my cock completely engulfed in a nice, hot vagina on those occasions I've found a female partner who could accommodate the head of my dick. Gay men, especially power bottoms, tend to have no problem taking in most of me. Still, not all.
Why anyone would want to pump their dick to the point of deforming it must fall into one of those sexual fetish categories I've yet to understand.