As the Maple protocol moves towards full decentralization, MPL holders will be responsible for governance. MPL holders can submit and vote on proposed changes to the protocol, including adjusting fees, minting or burning MPL Tokens, and other protocol level changes. If MPL holders don't want to participate in governance themselves, they'll have the option to delegate their voting rights.
MPL holders can also vote on distributing fees that have accrued to the Treasury. While this amount will be negligible at launch, it will grow as protocol usage grows.
You can view the MPL Scenario Calculator here.