Boosting not good? I take it you haven't used Eden yet...
Boosting can hurt you too. The number is the percentage of what it would normally do. Say Ifrit normally does about 500 HP of Damage. You mess up your boost at the last minute, so it goes back to 75. His attack only does 75% of what it normally does, so it'll do around 375 HP.
With Eden, the sequence is so long, that you can get it up to 250 (the maximum)