When you add an ID document that contains an address, we send that address to another identity verification provider. This is to ask them to confirm whether your address matches their records. If it doesn't, the check will fail. We do this to verify that you really do live there. The identity verification provider does not keep the details we send them. They simply check for a match and return a yes or no answer.
If you add your address manually, you can choose not to have your address verified. If you choose not to prove it, you can still add your address, but your address will be marked as ‘unverified’. But, some organisations might only accept checked addresses.