If you are running an old version of Windows it is absolutely vital that you keep your OS up to date. Many users of Windows 7 and XP have become lax in maintaining their Windows security patches and are in danger of becoming infected with malware.
As OS versions become End Of Life it may take extreme measures to patch it. For old Windows versions being used for critical operations it may become necessary to pay for Extended Support from Microsoft. (Extended Support for Windows 7 ends January 14, 2020.) For computers not connected to the Internet you may forget this because your machine is only endanger of attacks from people with physical access.
If you don’t want to shell out all that money for Extended Security Updates you can always upgrade to Windows 10 or even better try Linux.