People call Sakura useless without knowing what they are talking about. Tsunade doesn't amount to much more than a magical healing energy transmitter but you don't see anyone calling HER useless. She even nearly got her can handed to her by Kabuto.
Sakura is a MEDIC!!! She isn't supposed to be on the front lines risking her tail. She stays in the back making sure the people fighting stay in one piece. I play a support character in most MMOs I play and I can vouch that support characters (like Sakura) aren't supposed to throw themselves into the middle of a fight. We stay back and make sure the rest of the team stay healed. Going into battle without a healer is suicide.
I leave you with a philosophy from DBZAbridged:
If she goes down noone else is getting back up. That's right, she the White Mage, and you don't F*** with the white mage!
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