Fulfilling the Jail's 3 desires will net you a Jail Piece that can be used on the Jail Bonus roulette.

Some examples of available Jail Pieces:
・HP Heal Piece heals HP for 2 allies
・SP Heal Piece heals SP for 2 allies
・Damaging Piece deals damage to all enemies
・SP 1/3 Piece reduces SP use to 1/3 for 2 allies
・Gold Piece boosts Gold gained at results
・Unique Blood Crystal Pieces give you bonus crystals
Of course there are more than what's listed above.

Set these pieces using Jail Control to customize the roulette to play in your favor! You can even set up the roulette so that it only benefits you.
For example, you could set it up so that it will always fall on a healing effect!

Gather as many pieces as you can, and customize the roulette with Jail Control!