If you get a server of your own, it will work independently, so it will have its own Os and you could later install server side apps directly or script-driven sites via 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 may have better support for certain hardware, so you could get better performance for the internet sites and web apps you install. Your server shall also be more secure since updates normally include security patches that resolve small problems which may enable unauthorized people to access your content. Last, but not least, more modern script versions, which are also released for both enhanced security and for additional features, may require a later version of the Os in order to work correctly and with their full capabilities.