Each and every virtual or dedicated server has its own Os and works independently from the servers of other clients. Updating the Operating system is usually overlooked, but doing that could have lots of benefits for your sites. The most important reason to use the most up-to-date version is that patches are frequently released to fix security holes within the Operating System code, so if you don't install the updates, you risk people with harmful intentions to exploit these holes and to get access to your content. Operating system updates are also released for enhanced efficiency of the system in general and for much better compatibility with the hardware available on the market, which can directly influence the performance of your sites. If the efficiency and the security of your scripts is the reason to update them, you may also find out that their newest versions require an updated Operating System to be able to operate properly, so keeping the Operating system up-to-date is always wise.