One use case might be the presentation of an "exhibit" of an author's papers relating to a theme -- personal correspondence vs. professional correspondece, or political topics vs. business negotiations with an editor. Imagine Davidson's Complete Works of George Orwell divided into sets of "Wartime Broadcasts for the BBC", "Negotiations with Publishers", "Book and Pop-Culture Reviews", "Writing about WW2", "Papers relating to Animal Farm", and "Papers relating to 1984". In such a case, works would be selected from the collection on thematic lines, but many works would appear in two or more thematic sets.
Creation, editing, and assigning works to document sets will be, I hope, entirely straightforward. Nevertheless, I'm concerned about the possibility that documents may be made public accidentally. I've added indicator text about the default state of works and the public status of document sets, which I hope will prevent private material being made public. If you have any suggestions for making this clearer or easier to use, please let me know.