Rules for additional hands.

• Each hand is a separate zone.

• You may play cards from all of your hands.

• If you would draw a card or put a card into your hand, you choose which hand to put it.

• You cannot move cards between hands without explicit instructions.

• Maximum hand size is checked individually for each hand. If any hand exceeds max hand size during cleanup, discard cards from that hand until that hand meets max hand size.

• If an effect mentions your hand, you choose which hand it applies to. For example, an effect says "discard all cards from your hand", you discard all cards from one of your hands.

• If an effect would cause you to reveal your hand, you choose one hand to reveal. Further instructions of that effect applies only to the chosen hand.

• If an effect instructs you to discard without mentioning your hand, you must discard that many cards from among all cards in all of your hands. For example, "Discard a card", even if one of your hands is empty, you must discard a card from a nonempty hand.

How often would there be benefits to having multiple hands?

The fun is in figuring out how to abuse extra hands. The opening comment has some hints.

It just seems like a way to protect against getting certain cards discarded and an increased max handsize. Do you look at the card you draw before you add it to your hand?