YFI is the native token of the Yearn.Finance system. Yearn.Finance is a DeFi yield farming system, focused on making it easier for users to automatically farm the highest-yields possible with their cryptocurrency.
Yearn is a growing collection of DeFi services, intended to act as a simple gateway for the wider DeFi ecosystem.
Its centrepiece is the ability to automatically invest user deposits in the highest-yielding place available in the DeFi ecosystem, through Yearn Vaults. Users deposit funds into the vault, and those funds are then collectively allocated to the most lucrative yield farming available, and the returns from those are distributed proportionally to users, accumulating to the yTokens users are given when they make deposits.
Yearn can similarly let people make stablecoin deposits straight to the highest-yielding lending platform available, to earn competitive returns on stablecoins.
In addition to the ease of use, this also helps batch transactions to save on Ethereum gas fees. The service doesn't come for free though, as performance fees and other costs are extracted along the way. These fees can be paid to YFI token holders as dividends, in an amount the community of token holders agrees on.
YFI is purely and simply a governance token. Its holders are allowed to vote on decisions that affect Yearn.
While simple on paper, this can potentially be quite complex and lucrative though, as evidenced by the decision to receive a pay a cut of the service fees to token holders. And if Yearn becomes a prominent part of the DeFi world over time, other decisions such as support for different assets, and the way returns are paid or reinvested, could have profound impacts on the rest of the market over time. Yearn encourages YFI token holders to actively participate in governance.