I have for many years divided my main drive into three: C for Windows (yep, I can see the logic in hiding this elsewhere from hackers, but there it is) D for programs and E for...well, stuff. Vast areas of space space in C and D can be used for first stage backup of photos etc., (formatting would only mean the temporary loss of one of the backup strategies.)
I've never had much success in re-installing the OS and getting the programs working again without re-installing those as well.
What I can't understand, now that I'm not using good old F-Disk, Drive C & E have the Primary partition colour stripe showing over the allotted drive-spaces in Disk Management, while D shows a logical drive stripe with an extended (green) partition box round it. This seems counterintuitive.