Conveniently, the first person leaving might go to work for another company that has a similar policy, and start referring their co-workers from their previous

Conveniently, the first person leaving might go to work for another company that has a similar policy, and start referring their co-workers from their previous employer, who then move to the new employer, referring one another as they go. It is not quite a Ponzi scheme or chain letter, since (presumably) only one referrer could collect the bonus, but it might produce patterns where many people in one department follow the lead of the first one to migrate. OTOH, if the bonus is linked to the starting salary, HR may now have an incentive to low-ball the start, and then increase to retain. Cui bono?