Our use case is as follows: In our company, we have 80% of our computers running Linux. That's some 500 computers. The other 20% are Windows 7 to Windows 10 computers.
We use FreeIPA as the main source of user accounts. So we have set up Active Directory on the second server, to log users into Windows, and we need them to be able to log into the Windows systems using IPA credentials.
Two-way sync works fine, but for this reason we would need Outbound one-way sync.
So we need to authenticate the user credentials to the FreeIPA server. We don't need the reverse way - we don't want to authenticate users in AD