There's the consequences that might scare others into not overstaying. You may also be able to gain information from them that you could use to find others who

There's the consequences that might scare others into not overstaying. You may also be able to gain information from them that you could use to find others who aren't physically leaving the country. It's of course completely possible that there are unsavory and foul motives at work. It's also possible that there are things other than mass human rights violations that such a system might be useful for.