Hi @happyme

Here is the official statement on this from the whitepaper. I certainly hope this has not changed.

Payouts
When a post receives a payout it takes the form of 50% SBD and 50% SP. The Steem Power give the user increased voting and transaction power while the SBD gives the user an immediate benefit in a stable currency. As we’ve already discussed at length, SP is designed to encourage long-term holding rather than short-term selling. This encourages more users to have a vested interest in the long-term success of the
platform.

Users also have the option to be paid in 100% SP, as well as decline payout on posts. When a user declines payout on a post, the money that would have been paid to them remains in the rewards pool, to be distributed to other users.