If you get a server of your own, it will operate independently, so it'll have its own Os and you can later install server side applications directly or script-driven sites through a hosting Control Panel. Although keeping the Os updated isn't always considered a necessity, it can be a really important task for a variety of reasons. A more modern Operating system version might have better support for specific hardware, so you may get better performance for the sites and web apps that you install. Your server will also be more protected as updates normally include security patches that take care of small issues that may permit unauthorized people to access your content. Last, but not least, more modern script versions, which are also released for both improved security and for additional features, may need a later version of the Operating System in order to work correctly and with their 100 % capabilities.