It can also break compatibility. I built a PC for the first time in probably 10 years. I went with Windows 10, but most of the my stuff didn't have drivers and support. I couldn't tell if things were broken or just didn't have driver support. I cobbled together a version of Windows 7 to make sure everything worked, then moved back to Windows 10.

South Park Studios still uses an image compositor called Shake. It's cross platform (OSX, Windows, Linux) and Apple stopped development in 2008, but they still use Shake to make new episodes. There's a good chance it won't run on the latest version of the operating system, but they've made a huge investment in software and hardware that works fine. Forcing and update would shut down production.