Right now, you can have rewards sent to one of three destinations:

• Stash, staked
• Stash, free
• Controller

We should add the option for the stash to designate a beneficiary account.

Problem with sending to stash: The stash is supposed to be as cold as possible. Ideally, the only transactions it ever submits are bond and set_controller. However, validators will have to liquidate some of their rewards to pay operating costs. If rewards are sent to the stash, then they will have to make a monthly transfer, making the stash keys warm.

Why not send to the controller? Some staking service providers are operating the controller for their clients so that the client doesn't have to manage session keys. The staker wouldn't want to send rewards to the service company because it will add a delay to receiving them, and the service company probably doesn't want them from a tax/accounting perspective.

It would be best to have the option to designate a beneficiary account that the staker can send rewards to. From there they can do what they please, for example liquidate some portion and transfer the rest to a cold account for savings.