Depends on the quest. If you HAVE to kill to progress a good zerger will use that tactic. But in quests that don't require it, its faster and more xp/minute to ignore the mobs or just throw out a web as you run. Get to end, kill boss, throw up a dimension door then recall/ walk out the entrance. This is what DA was designed to prevent. Unfortunately it has had unintended side effects, the worse being how you can get instant da even when killing everything.