If you get a server of your own, it will operate independently, so it'll have its own Os and you could later install server side apps directly or script-driven sites through a hosting Control Panel. While keeping the Os updated isn't always considered a necessity, it can be a very important task for a variety of reasons. A more modern OS version might have better support for specific hardware, so you might get better performance for the sites and web applications which you install. Your server shall also be more safe since updates usually include security patches that resolve small problems which may permit unauthorized people to access your content. Last, but not least, more recent script versions, which are also released for both improved security and for additional features, may need a later version of the Os in order to work properly and with their full capabilities.