Depends on the dungeon, as many people said.
In Library (Hard) for example, the dungeon is short and the mobs die faster. Going in as DRK, if my party's DPS is a combination of BLM, SMN, BRD or MCH, I'm excited and will mass pull. Otherwise, I pull the first two groups and determine if I can keep pulling. I judge this based on Blood Price; mobs should be dead before Blood Price is active a second time in the same group of mobs.
I don't do it too much in the Leveling or Lv50 dungeons, as I don't have access to Abyssal Drain.
