I just upgraded my main hard disk to an SSD. I installed and re-activated Windows 10 on the SSD. Now I have a old hard disk that I want to use as storage. It already has some files that I want to keep. So I was thinking that I can just delete all the Windows-related folders and start using it for purely storage. For example, I could delete the following files (outlined in red) and keep the "Users" folder which has the files that I want to keep.
However, there was at least one article I found that mentioned reformatting the disk without explaining why. So that left me curious. Is there any particular reason to reformat an old hard disk before using it as storage?