She brought up ret paladins... they don't do as much damage sustained as a similarly geared rogue would, but they provide a lot of group utility and buffs and auras, and they're wearing plate, so they tend to be more durable than rogues, requiring less healing. But the rogue, despite potentially costing more in terms of healing and often using items like Haste Potions, generates quite a bit of DPS, so that if you take into account the amount of damage he does vs. what it takes to keep him up doing it and what he has to spend to do it at peak, it might still be better to bring the high sustained mana-free rogue over the mana-dependent paladin. Or it might not be. Honestly, she lost me at the point where she started talking about co-efficients.
We started talking about all the different classes and what they have to do or have to be competitive... warriors need buffs from outside like Blessing of Kings and Windfury totem, hunters need ammo and food for their pets, mages are pretty low-maintenance but are still chugging mana pots and mana gems, warlocks can life tap and drain life but are still at risk and need some healer attention... and we didn't come up with any conclusions. I found it interesting to consider the idea, though: when I DPS, how 'cost-effective' am I versus another class? How much in consumables, how much time and effort from other players does it take for me to generate the damage? And how would you rate your own class, are you 'economy' DPS, cheap to keep going, or 'luxury' DPS, requiring a lot of upkeep but bringing higher performance, or are these even valid considerations?