Each 1000 HP delegated nets 1 young citizen per day, and each 200 HP delegated gets a 'lottery ticket' for a daily Influencer citizen raffle. Additionally, there are some SIM rewards, approximately 7% apr right now.
These rewards are subject to change, right now in SIM club discussion channel, there is some debate to replace the 7% SIM apr with a second Young Citizen daily, meaning it would be every 500 HP delegated, get 1 Young Citizen daily, and no SIM rewards. I don't know how fast this change might be debated, voted on and implemented, but it is in the discussion.
The curation rewards on the account are used to buy SIM on the market.