The only fighter I know of who did this was "Neon" Leon Spinks, who went from Heavyweight champion, down to cruiserweight, after he failed to make good as a Heavywieght---and failed in the process to become anything at Cruiser.
Wouldn't that be more a negative than a positive to go down in weight? Cus wouldnt that expell your energy? I mean, look at Antonio Tarver, he went up to 210 pounds to be Mason "The Line" Dixon in Rocky 6, then faced over-blown Bernard Hopkins and lost, after he had to lose the bulk.
Roy Jones had a bad performance against Tarver, after he ballooned to Heavyweight against John Ruiz, only to go back to Light Heavyweight.
