Originally posted by Not a Number Running the upgrade from Windows (online or from downloaded media) gives you the option to keep your apps and data otherwise it gets wiped. The upgrade process will update all your drivers and flag any incompatible programs. Indeed it actually re-installs much of you old software. The old driver store and Windows program gets left in the Windows.old. It basically saves you having to reinstall all your apps and hunt down drivers and install.
I wasn't aware that a clean-install can be done with the old WIN7/8 keys, good to know!
I keep images of my Windows at different stages and often go back to an early image because it is clean.
Of course it has to be updated but it is so obvious how much better a clean system works.