So say your in a area that gives you a check point. And in this area is a Rare(Yellow) mob. You go over and kill it, then loot it. You leave the game and then re-enter and you are back in the previous check point you were just at and the Rare mob in the area is alive again. (Just different name and whatever effect it attacks with.) Kill it again and get more loot.
Granted its usually not an AMAZING item... but you usually get 1-2 blues per kill. Now Ive only done this a couple of times, but it seems like you can do it as many times as you want. If so... it might be a good idea to maybe have like a 10-15 min loot lock or something along those lines. Like you could kill the rare again if you wanted but you wouldnt get any magic items for a set period of time.
Im just taking note of this. No idea if its been addressed or if its just fine that way. My only issue would be mass item generation that could potential affect say the AH and cause inflation and so forth. Its unlikely but just thought Id mention it.