Hi Jon,
You may need a Windows 10 computer with Fall Creators Update to use the Files On-Demand feature in the new OneDrive sync client to save all files online not locally.
For your reference: https://support.office.com/en-us/article/learn-about-onedrive-files-on-demand-0e6860d3-d9f3-4971-b321-7092438fb38e
Thanks,
Cliff