The only airlines that I've been on where it has made a difference having priority tags have been QF and NZ, where the priority bags seem to be in their own containers, and those containers are off-loaded and delivered with before the others are touched, quite often the bags are on the carousel before you get through Immigration, Customs, and Agriculture. I suppose this is one of the benefits of pay ten grand for a ticket. Also QF even adds the tags to bags if you are connecting from AC in LAX even though you never see the bags, but just give the agent the tags.