It's super easy to start syncing. Then it gets hard. Noting in the context menu under root for SharePoint sync where it would be intuitively and should be. If a doc lib -is- there and not synced anymore for whatever reason (lost access, error, stopped syncing) then the folder/files should get a warning flag. People continue to work in the documents thinking they are collaborating and confusion is everywhere.
And if someone stops to sync, then the local files should be 1) offloaded and then 2) stop sync to not leave any residue.
Working with training and adoption this is a HUGE deal.
this is a huge source of helpdesk tickets. the other issue is people deleting folders when they are still sync'd. We have done training, written documents, FAQs, etc. If the user has the choice to View Online, Keep a Local Copy and other options to manage onedrive when they right click, maybe Stop Sync could be added there