It dos when you have a resto shaman and a druid there, you get WF from the resto shaman... you get HP and Mana for the healers... they are not realy needed in group one, the pala will have egnuff mana to last the fights... the mage maby want to drink and doomkin, but they get a good dps boost from the warlock and the 5% crit from moonkin and they also get a boost from the shadowpriest in the other group ( shadow damage)
and you get 3% more crit from the elemental shaman +100 spell damage...
The dps can sit and rest wile pulling but the healers shud have mana all the time and therefor have a spriest to boost mana regen...