Liquidity pools are a requirement for all AMMs. These allow them to offer the service of decentralised swapping. Having a deep liquidity ensures trades can be facilitated at a larger size and greater volume. All swaps take a fee proportional to the size of the trade. These are then rendered to liquidity providers (0.25%) and xSushi holders (0.05%). The higher the trade volume, the larger the APR on your xSushi stakings.