Revisit great, rejected applications
Sometimes a great applicant comes along but the timing isn’t right. You might have just filled an open role with another candidate, or this great applicant could be good for your company overall, but not quite right for an open role.
In 2010, Google ran an experiment to revisit some of the rejected software engineer resumes that were borderline cases. These borderline candidates had a few more years of experience and Google's hiring needs had evolved.
This showed the hiring team that it’s critical to give all candidates, even those you reject, a great application experience. They may be potential hires in the future.