Revision control in the context of Flatter Files is focused on providing a review process and revision history that actually improves the workflow instead of merely causing paperwork hurdles that result in decreased productivity.  When editing begins, the drawing is checked out.  The CAD professional can either do this manually with one click or it can be done automatically when the drawing is first saved.  When a drawing is checked out, anyone viewing the drawing will be notified that it is checked out.  Once editing is finished and the drawing is automatically uploaded the CAD Professional simply checks the drawing in and selects a reviewer.  The reviewer is them sent a review notification.  Once the reviewer accepts the drawing a new revision is created.  The revisions are permanently saved and anytime a drawing is being reviewed all previous versions can be viewed by a simple click.

See this post for further details regarding the overall workflow for the CAD Professional.