What Does “Always Authenticate” Do?

The ‘always authenticate’ option was added to deal with the case where user X may have read access to a share but no write access, unless X authenticates explicitly. This occurs for example when shares are opened to everyone for reading but only certain users have write access.

BackupChain is then forced to re-authenticate to ensure user X is treated as user X and not as ‘everyone’ or anonymous.

Please also note that Microsoft Windows does not permit accessing the same network server (perhaps two separate shares) via two different user accounts, even if you used another user session.