Mac OS X Server was..

.. macOS but with a utility to install apache/ldap/smtp/carddav and caldav.

very useful for a home server.

absolutely no benefit over Linux for the majority of the workloads it was designed to simplify.

It wouldn't really give you much unfortunately, certainly didn't run noticeably leaner.

(I think at some point "server" just became an .app that was available via the app store).