Mana access during a battle.

[Nitelite]

I always wondered this as well. With mana potions, if you have the time after a fight to quaff a potion, chances are you had the time to get yourself out of the way of a back to back fight. Outside of just speeding up gameplay, I can't see any advantage.

Rage potions are different because it gives you something you cannot gain by standing idle or maneuvering around.