Reformatted Windows 7. Do I need to keep Old Windows folder on C Drive(4 posts)
Windows.old basically contains all the important files and short intro about programs that you use in previous version of Windows. If you haven't any important files or product keys that you want to have in future, you may directly delete the whole folder.
Remember, few program needs you to enter the product key after clean installation of Windows and if you haven't taken backup of it, you may need to pay money to have the key.