Heroes 3 in the cloud.

Tip: Don't store any of your files on the C: drive – that way, you won't lose anything if you reinstall the OS (or encounter other problems)!

This is advice from the early 2000s, when hard drives were much smaller.
Of course, this might seem like the "right" way to do things, but what prevents you from connecting this hard drive as an additional drive? Having only one hard drive in a computer is no longer standard.