User blog comment:Ozuar/The 9 Health Potion Argument/@comment-5686533-20130423082609/@comment-9713132-20130423111013

It's not so one-dimensional though - champions with already high base health regeneration will basically negate your nuke if they manage to survive it, and start farming / zoning again in no more than 20 seconds. They've technically lost nothing, because you've expended your mana for little gain and if they can play smart, they'll repeat the strategy on you and because you have no mana now, you'll be forced to recall.

Of course, there are exceptions such as, I dunno, Soraka who can bring mana pots and heal herself up, or Akali, who doesn't use mana, but the rules go - 9 pots basically allows them to survive and come back into lane after what (in a balanced game) should've forced you to recall.