When uploading to onedrive for business two versions of every file are created. That means that for every 1MB of backups 2MB of storage is used.

This was tested on the latest 1.38 beta on Linux and 1.38 stable on Windows and Linux.

Here you can see that the used space is double the size of the file:

And here you can see the culprit, two versions of the same file from the same upload:

More info:
https://forum.rclone.org/t/onedrive-for-business-uses-2x-the-space/3971/8