(reference to SpongeBob) The first discarded hand is kept in a limbo state, represented by each card floating in a bubble to the side of the screen. You can select any of these cards for use in a hand, but doing so pops the bubble and discards the rest of the unused cards. Kept in hand effects do not work for cards held in a bubble.
I can see this joker being useful for when you have a really good hand, but you wanna fish for better cards (like some steel cards or an even better hand).