amen mountdoug,
the idea is that the jacketed bullet, being harder, will burnish some of the burs left in the machining process. but, it is also copper that fouls the bore at the same time, due to the same burs. so ifin you shoot, clean, shoot, clean... what you should get is a smooth polished bore were it will be mutch harder for the copper and powder to build up in the future, and MUTCH easier to clean, as there won't be all the nooks and cranies for the copper and powder to build up in.
if you just shoot shoot shoot, you just fill the nooks and cranies up with copper fouling, and never properly season the bore, and then wonder why it always takes so long to get clean patches out of the barrel. they may not come out black, but how about green?