>>Which can be an advantage. I've been wasting a month battling a bug in the ARG library that got introduced in a Windows 10 update. If there are no updates there is less chance it will break something along the way.
>
>Can also be a disadvantage

At that rate, he might as well stick with XP (i.e. not just himself, but all his customers as well) -- to be "immune" from updates. Obvious disadvantage of course is that you're setting yourself up for getting trapped.

As for my own reasons for *not* taking up the free offer to Windows 7 to Windows 10 -- they happen to be:
* I'd lose XP mode VM (although I could simply set up a VM as long as I've got a valid XP license -- the hitch being that XP licenses are in short supply). I might not use it all the time, but I do on occasion have situations where it's come in handy when dealing with legacy software (often 16-bit variety).
* I'd like to retain at least one computer with Windows 7 mostly for compatibility testing as well as having something that I can use in walking a customer through various processes.
When I do replace this particular computer, I'm not planning to ask for "downgrade" to Windows 7

As for why I might want to use legacy software -- mainly for dealing with older file formats which may no longer be supported in current software. Ever try opening older WRI or RTF files that originated from a Win16 environment (although you can generally retrieve the textual information -- you do lose the formatting as well as any graphical content) ?