My small music related business used to run a Mac Pro 1,1 on Snow Leopard Server as the major file server. It was easily the most stable piece of hardware + OS that I have ever used. I set it up initially with the intention of just test running it, ended up getting the SMB server running and imported the list of users in like half an hour, actually deployed it right afterwards, never even needed to reboot once for the following 3 years or so. Mind you I got no IT background, just a business owner with some Macs experience. It got other server functions pre-cloud that were really handy, like the CardDAV and CalDAV servers, of course Time Machine, and your standard stuff like Apache / FTP etc. Granted many of these are "easy" to be done via commandline or some 3rd party app, but having everything in a single OS with a single pane of glass, with human-readable interface was really helpful. Not to mention being a server OS it cut the fat compared to a client OS, Snow Leopard client was already extremely stable, and the server variant made it even more so.
I really miss the days when Apple was visibly competent as a tech company. Nowdays we moved on to Synology for servers, and Ubiquiti for network appliances (mourning AirPort Extremes...)