Lightroom Journal: Use Worklist Keywords to Help Your Keywording in Lightroom
blogs.adobe.com/lightroomjournal/2007/09/use_worklist_keywords_to_help_1.html
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
So you want to make sure you've identified all of the people you know in your Lightroom catalog, but ... you have several thousand photos in your catalog and you don't want to spend time reviewing photos you've already keyworded. How to avoid that?