Its important to back up your wallet so that you can recover your wallet in case of disaster
If all funds have been removed from your wallet and you do not wish to have the wallet data stored on your computer anymore, you can delete your wallet.
Your master private key contains the information to sign any transaction on this wallet. Handle with care.
This will scan the blockchain looking for addresses derived from your wallet, in case you have funds in addresses not yet generated (e.g.: you restored an old backup).