Salvaging and re-using primers DOES seem like a waste of time.
HOWEVER, there are some circumstances where it is justified:
During WWII, Filipino (and elsewhere) guerilla war fighters reused FIRED primer cups and anvils by depriming, tapping out the indentation, and refilling with home-made priming compound, black powder, and cut-down bolts for bullets. Sounds like desperation, doesn't it? Well, it WAS!
Fred Barnes, author of Cartridges of the World, wrote that during the civilian ammo shortages of WWII, a friend salvaged M1 carbine ammunition by laboriously sawing cases in half to get the intact primers, and reloaded .357 ammunition using the primers and powder. He kept his S&W firing when no one else could get or make ammo.