A Smart Wallet is a DSProxy smart contract wallet that is created, owned, and accessible by you and only you. This contract allows for complex, multi-step interactions to be executed in a single transaction. That means it is essential for our signature advanced management features - Boost & Repay. It can also be used to potentially allow other services to execute transactions on your behalf, which is the case with our flagship feature Automation (once we add support for Liquity Automation).
You can learn more about it here: https://help.defisaver.com/general/what-is-the-smart-wallet