Telling someone their work is not good enough is nobody's favorite part of the job, and no framework makes it pleasant. This one at least makes it routine. In a regular check-in you name what the person should keep doing, what they should hand off or drop, and what they should take on instead. Because it happens on a schedule, nobody feels singled out when their turn comes.
This is the short version. The full lesson, with the story behind it, is in the book.
Take The Summer Camp MBA with you, or get the field notes by email while you work through the lessons here.