Here's what Solana Docs have to say on Stake Pools:
"This on-chain program pools together SOL to be staked by a manager, allowing SOL holders to stake and earn rewards without managing stakes. Users deposit SOL in exchange for SPL tokens (staking derivatives) that represent their ownership in the stake pool. The pool manager stakes deposited SOL according to their strategy, perhaps using a variant of an auto-delegation bot as described above. As stakes earn rewards, the pool and pool tokens grow proportionally in value. Finally, pool token holders can send SPL tokens back to the stake pool to redeem SOL, thereby participating in decentralization with much less work required."