I was in a random group with three people who were obviously together, one DPS of appropriate level, a higher level healer and max level ICC entry geared tank. Neither the healer or tank even spoke, but it was apparent they were talking amongst themselves through some other medium, probably vent.
So the DPS calls out at the beginning of the instance that they will be making "big pulls". This is after a fairly long pause waiting for the healer to zone in. We are doing Utgarde Keep and the tank proceeds to pull the first two, and that is all.
The tank then runs in and grabs half the room where most tanks grab the whole thing. Pats come by and pull the rest of the room, mobs go straight for the healer and I'm starting to pull aggro on my level 70 pally from a 5k+ gearscore tank. Big pulls, yeah right.
So the next pull the tank whacks the single then runs off to grab more without any warning. The other DPS and I who weren’t in communication with the tank both pulled aggro, I stunned the mob and the tank came back to "tank" it while it was stunned. Next couple pulls were single groups again; then came the room with the drakes.
The tank pulls a single drake, stays there a second then takes off to grab the next group, again without any warning. I had aggro on that single drake pretty quick and being on a pally managed to bubble and stay alive. Obviously big pulls means randomly choosing to tank and not tank certain mobs.
The rest of the instance was much of the same with some oddly long pauses where the tank and healer would sit around the recently dead mobs and say a prayer or something. It was a very slow moving PUG even compared to the usual level 68-70 groups.
This was just another example of how pulling big is not something that should be executed by an inexperienced tank. Pulling additional mobs is something tanks learn to do over time by anticipating what their group can handle and more importantly what they can maintain control of. Big pulls are a pretty stupid idea in general as they are hard for DPS to anticipate without some communication from the tank and more often than not are less efficient than timely single pulls.
The more appropriate tactic for speeding up an instance is called chain pulling. Once you have adequate threat on one group of mobs you go ahead and grab the next, moving along at a constant steady pace. The DPS never stop which makes things go considerably faster opposed to waiting for a tank to gather a large group while the DPS does nothing in that time. It takes a very large AOE group to make up for a long wait time of zero DPS when it comes to average DPS.
The main thing to gauge your chain pulling speed by is your healer's mana, DPS mana is unimportant (even if they do complain about it). If your healer is doing OK mana wise then your DPS should be too, otherwise they are doing something wrong (most likely going all out on trash instead of doing slightly lower sustainable damage). In any case your affected DPS can hang back and drink while you move forward. The exception to the DPS mana rule is that it is often a good idea to let everyone start a boss at full mana, but that is only until you outlevel or overgear the content.