In addition to collecting interest from lending and fees from market making, the protocol automatically claims and converts the bonus incentives that are being distributed by many of the DeFi protocols. For example, Compound gives away COMP tokens and Curve gives away CRV tokens. These bonus rewards are regularly converted into the backing collateral (stables for OUSD, LSTs & ETH for OETH), and distributed to token holders in the form of additional yield.
The harvesting of these rewards is completely decentralized and open for anyone to participate. The protocol offers 1% of the claimed rewards as an incentive to whoever is willing to call the function first. You can think of it as a reverse auction, whereby the protocol finds whoever is willing to accept the lowest price for the work that is being performed. View the Incentivised Harvesting Guide for details on how to participate.
Today, rewards are a significant factor for yield farmers as they represent a large percentage of their returns. The market value of the various rewards being offered should be considered when voting on how to best allocate resources between strategies.