In the case of Smart Pools, the tokens are used in an automated market maker which maintains their set percentage allocation as users interact with the liquidity pool. Swap fees from interactions with the pools are gathered for pie holders, constantly growing their balances.
What is a PieVault?
PieVaults can be seen as the next generation of PieDAO products. Instead of being fixed percentage AMMs, PieVaults actively employ each of the underlying assets with a yield-generating strategy.