Exactly as 3JPLW mentioned, government agencies value the polygraph as an aid to interrogation. Naïve and gullible persons, be they applicants for government jobs, criminal suspects, or criminals released on probation or parole, will sometimes make admissions that they might not otherwise make, because the fear that the polygraph can read their mind convinces them that their best choice is to confess.

But the polygraph can only have such utility so long as the general public believes that it can detect lies. We're at the point now that applicants for public jobs who face polygraph screening are often being specifically instructed not to research polygraphy.