When connecting Unix machines through SSH,the SSH Slaves plugin uses the SSH Credentials plugin to be able to store the SSH credentials in one place. Then when or if these credentials change, they only have to be updated in one place to update every affected SSH slave connected.
However, when adding a Windows slave, using the "Let Jenkins Control this Windows Slave as Windows service" method, each slave connected has its own authentication credentials. This means after a password change that every Windows slave configuration must be updated. These credentials for Windows slaves should be stored in the Credentials Manager plugin, and used from there, then the storing of credentials for Windows or Unix slaves would be consistent, and the maintenance of Windows slaves would be reduced.