If you are in an open zone and the crap the people are running by isn't even in the same level as your mission, what is the point in hanging around and killing it all? Leave that to the guys trying to kill that stuff in Patrols. That is what they are there for. Once you passed a certain point, none of those mobs are going to try to kill you anyway, so it isn't making it any harder except for you, wanting to hang back.