[Noseshine]

No, his point is that if you are lying they have an instrument to use against you. Similar to how they got Al Capone, where they didn't have to go through the trouble of having to prove his actual crimes in court.

It isn't about you individually, it's about big numbers, statistics. It's just an additional tool in their arsenal. Similar to why doctors perform standard exams even when you come in and complain about something where that particular exam seems ridiculously wrong. The procedures are not invented new each time for every person, they are based on what works "statistically". On that level they found that in (some low) x percent of cases having such a signature helps, so they include that question. And occasionally they even catch someone gullible to, or who can't manage their emotions, but that's just an additional bonus and not even the main reason for the question(s).