I'm too lazy to do a search, but I'm sure you can find a million threads on this very topic. Back when I was PM (those were the days ), I tried an experiment since I fly to DAB alot. I'd check bags with and without the PM Priority tags. Believe it or not, in every case, my bags came our FASTER without the PM Priority tags! In fact, one time, my bags with the PM Priority tags were immediately followed by the "last bag on flight" sign I've had similar experiences with international flights.

No, Delta does NOT have to go rummaging through the baggage holds to find priority bags first. All they have to do is segregate the priority bags before loading the aircraft and either load them last, or load them into a baggage hold that will be unloaded first. Other airlines seem to have mastered handling priority baggage, and I've given up on trying to figure out why it's such a mystery for Delta.