Microsoft is making some important changes to reduce the chances of losing Office documents as a result of malware or problems with your device by offering to save your files directly into the OneDrive folder by default.
Using the Known Folder Move (KFM) feature already available in OneDrive, the next time you save a Word, Excel, or PowerPoint document, it’ll save automatically in the cloud.
After updating your Office 365 apps to the latest version, when clicking the Save button or using the Ctrl + S keyboard shortcut, you’ll see a new save experience that will default to your OneDrive or SharePoint folder.
OneDrive default location for Office documents
Furthermore, if you try to close an app without saving its content, Office will alert you and give you a choice to save the documents to OneDrive or any other folder.
The new feature is coming to Windows 10 as well as for macOS in February, and until then, make sure to save your documents as soon as you create them.