User blog comment:Zambu/Useless passives/@comment-4794115-20130501183133/@comment-4794115-20130501195457

The old passive was less useful. With the old passive, people would stack regen instead of flat mana. So you get some abilities off, wait, abilities, wait.

Like I said, the new passive is more of an encouragement to build mana on taric. Flat mana allows you to just Q all the time WITHOUT having to sit there and beat on someone when it could be dangerous to do so.

It's like how blitz's passive makes mana stacking somewhat necessary. Items like FH or IBG or now way stronger on taric, making him better at being tanky.