Vote delegation lets token holders transfer their voting power to another user, while maintaining control of the underlying governance token. Delegation can be withdrawn at any time, which helps ensure that delegates remain aligned with their supporters.
Delegation lowers the cost of participating in governance. Token holders can avoid the time involved in reviewing each individual proposal, as well as the transaction fee required to submit their vote on chain. However, there is still a transaction cost associated with delegating/undelegating for most protocols.
Delegation can also help amplify the voice of smaller token holders. Many protocols have minimum vote requirements to submit and pass proposals. As such, smaller token holders can delegate their voting power to one or a few delegates to propose and vote on their behalf.
For some protocols, you need to delegate your voting rights to yourself in order to participate in governance on your own account.