To my understanding, zerging can be most simply described as getting through from quest beginning to completion in the most efficient mannor possible. Drag mobs till they rebound or arrive at a predetermined kill zone. Really only effective when you know a quest well enough to: A) predetermine where said kill zones are, B) what specific gear you need (ie. having{knowing what} a sufficient # of invis clickies is) C) know the map so as to avoid taking any "long ways around" D)probably some stuff I'm not thinking of ATM.
I believe newer players don't like this for lots of reasons, such as they want to do something really weird like, *gasp* explore a new environment. So they join or put up an lfm, then some TR toaster enters the quest and finishes it in a flash, leaving the new people A) bewildered about what just happened & B) saddend that any further time spent in the quest yields no rewards (no ransack/onslaught/trap bonous), and disappointed that they didn't even get to see the boss, let alone play with it.
Yes, I said play.
While some people get the most enjoyment out of crushing content in as dominant a manor as possible, others like to poke around, explore and experience what they (may have) paid for.
Also an (I feel) often overlooked situation is that non-VIPs often have limited access to content, and may be more interested in maximizing xp/quest than xp/min. So they put up an lfm and someone joins & zergs it "doing them the favor of completing it fast" and leaves the poster annoyed at not getting the amount of xp they expected or needed from a run with complete opts/ ransack/ etc...
Obviously these are situations that could've worked out better with sufficient communication, but that's a whole 'nother thread
