If you refer to O365 and its OneDrive component;
OneDrive is not a backup, it’s a cloud location of your data.
The default installation of Office 365 and its OneDrive component uploads all the contents of the PC \My Documents\ folders to OneDrive, (syncs) and there will be a OneDrive folder in File Explorer containing all the OneDrive content. And in Word etc the default Save location is set to OneDrive.
No Docs/data is stored on the local PC
The OneDrive included in win only has a 5gb capacity and nothing is added to it unless done by the user