Keep Old Software in Case of Need
Problems happen. Have tools to fix them. Operating systems (OSes) are a good part of a toolkit.
Linux is free and capable. I rescued a machine because I have an old version of Knoppix Linux that supports wireless networking when a new Fedora Linux got too complicated to set up for wireless. The difference is often with hardware that might be obsolete, for which an old program is a perfect fit. Sometimes, newer software versions no longer support a technology. I installed Knoppix temporarily, so I could download a newer operating system from someone else, so I’d have something that may be up to date against new security threats.
Microsoft products might be okay, but many of their licenses forbid what you need to do. If you’ve already upgraded Windows, you’re not allowed to use the old Windows without the upgrade anymore, unless you buy a downgrade license, and I don’t know how much that costs. Also, if you have a Windows disc for only one user (the usual way it’s sold) and installed it onto one machine, you can’t use the disc on another machine at the same time. But Linux is liberally licensed and you can ignore upgrades and simultaneous use without violating anything.
I still have Windows 98SE discs (as of 2017), roughly twenty years after they came on sale. I’m still trying to figure out what to do with them, without throwing them away. They shouldn’t be used on the Internet. I had at least one 98SE machine running maybe five years ago, making itself useful.