A small liquidity provider fee is taken out of each trade and added to the reserves. While the ETH-ERC20 reserve ratio is constantly shifting, fees make sure that the total combined reserve size increases with every trade. This functions as a payout to liquidity providers that is collected when they burn their pool tokens to withdraw their portion of total reserves. Guaranteed arbitrage opportunities from price fluctuations should push a steady flow of transactions through the system and increase the amount of fee revenue generated.