Please understand this is just my opinion but I am rather firm in it.
Clamping: obviously puts stress on almost all tissues from an internal point of view. I think this is one of the best girth exercise applications a guy can utilize. It is blood driven so pressures increase the size of blood holding structures directly. It expands the corpus cavernosa, it dilates blood vessels, and internally pressures the glans.
Pumping: I consider pumping a complete waste of time. All it does is bring in and congregate lymphatic fluid in the skin. It might deposit some of the same fluids inside around other structures but the end result is always the same and that is NO GROWTH. These fluids leave the area within 24 hours and you are back to where you started, no gain, even over a long period of time and may applications. Case in point is a recent new member here at Thunder’s that had been pumping for 6 years. He testified that of all the time he had spent pumping he had NO GROWTH as a result and was happy he had found Thunders to give him something that worked. We won’t go into specifics here. The point is there is only one good use (as I see it) for a pump and that is a very consistent measurement device. Once you reach a level of vacuum for a specific period of time the lenght you have will be an absolute. You can not lie about length while in the tube, even to yourself it’s either there or it isn’t. I have relegated myself to a once a month measurement. That’s when I break out the tube and find out reality. Pumping gives you the feeling that you are getting more volume, and you are, but it is false volume that quickly dissipates, but it is fun for the short run. It even might be OK for a quick go with the wife after and she might enjoy it but don’t expect it to be there the next morning or afternoon.
I know pumper’s out there will have a different opinion but my experience doesn’t indicate a long lasting benefit to pumping.