What is macOS Server Good For?
macOS Server is now basically an MDM server, powerful in its own right, but all the traditional things we used to associate with Server, like network services, Open Directory, file serving, caching update server, i.e. the good old days, is gone.

Server is geared now for education and business customers to maintain, administer and provision macOS and iOS devices. It scales down to providing much finer control of provisioning and administering iDevices and macOS machines for a large Apple-centric family with kids of several ages, for example.