With Sharepoint and Onedrive locally downloading every file a user opens, it can lead to the C drive running out of space.
To send all the locally saved files backup to the cloud you can choose the clear space option within Onedrive.
It will take a while to kick in but once it starts to sync it does free up space on the c drive. After a few hours there should be sufficient space again.
Right click on the users top level Onedrive folder and select the option
