Only when there's a reason to:
- New build
- Something's seriously broken
- To pass on an old PC to someone else
Otherwise "it aint broke don't fix it".
(emphasis mine)
Oh if that were only the case.
That's just the problem. I view the endless Windows slowdown to very much inhibit my ability to use the machine, which lands it squarely in the "seriously broken" category.
Ever since Windows 3.11WFW I've been told that Windows machines simply "don't slow down" that it's entirely all the software I install, or some virus. This is, as far as I can tell, an enormous crock.
So to answer the OP's question:
1. Every year or so I want to.
2. I procrastinate and end up doing it every 3 years or so.
My XP installations, for instance, were likely the most bulletproof of all the Windows rev's I've had experience with (Entirely my own opinion, and of course, subject to multiple factors, so who knows if it truly was).
Contrast this with Linux, where I install it, and it never ever seems to behave any differently. And this is no mere confirmation bias. It's just not a complaint anyone hears. Note: I'm not a fan of
capitalism killing free software, but my background is in Unix, so it's pretty much home to me.