Bon-Bon is welcome to your service when you become more experienced at the game. Like for example, when your fighting the 2nd/3rd boss of the game, they may be too strong for your characters. Not a problem for Bon-Bon, because Ribbon Dance saps their HP and in return gives one of your allies or herself HP, so they can continue fighting. She contributes to the story alot. She never died in the story :D
Credit to WilliDGamer.
