My Mini just runs iTunes 24/7 with homesharing enabled and a library of about 4000 songs, 600 movies and 600 TV show. That's what I consider an "iTunes Server"
An Apple Music subscription would not give me access to movies and TV shows, especially many obscure ones I have ripped from DVD or downloaded from places like archive.org. And I don't think Apple Music would give me access to the hundreds of hours of similarly obscure music in my library.
But probably... if you have to ask... you don't need it, it's not for everyone. My son in law says he has almost exclusively switched to Apple Music, although we always have fun listening to the obscure music and watching the rare movies when they visit.