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 programs directly or script-driven websites through a hosting Control Panel. While keeping the Operating System updated is not always considered an absolute necessity, it can be a rather important task for a variety of reasons. A more modern OS version could have better support for certain hardware, so you could get better performance for the websites and web apps that you install. Your server will also be more safe since updates usually include security patches that deal with small issues which may allow unauthorized people to access your content. Last, but not least, more modern script versions, which are also released for both increased security and for additional features, may need a later version of the Os in order to work correctly and with their 100 % capabilities.