At home, I reinstall when I make a significant hardware change, like replacing the motherboard or getting a different storage controller. I reinstalled a bunch of times when testing Linux on desktop, but that's a testing environment so I don't think that counts.
At work, and on a relative's PC, I had to reinstall Windows 10 too many times. It's the same scenario each time. The system tries installing an update, the update takes forever, then randomly the system shuts down, and now the OS is broken, and your user files may or may not be recoverable. I think it was a bug that was fixed. It happened somewhere between the 1607 and 1809 builds in work, and 1607 LTSB on the relative's PC.
Back in the 98/XP days, I had to reinstall a few times due to the system getting oddly slow to startup, but I don't know if that was necessary. It felt better starting with an updated CD/ISO. It hasn't been a problem since I switched to SSDs. Maybe it was the HDDs getting fragmented.