Back when I was in college, one year I supported myself by working the graveyard shift at a 24 hour gas station, quick mart.
I was a good job for a student. I worked alone and as a result didn't have many responsibilities. In the 8 hour shift I was expected to make sure the cooler was stocked, the floor got mopped, and I didn't get killed.
After about 1am on most nights there was almost no traffic ( one or two people tops ) and if gave me a lot of time to study for class.
One very unpleasant aspect of the job was everyone who worked for the company was required to take a lie detector test every 3 months. This company has their own little testing room set up in the main office.
When I quit this job at the end of the school year (for real daytime work over the summer), the manager of the company took me into his confidence.
The lie detector was a useless tool for them. They didn't expect to find out liars or thieves by looking at the test data. He said that everyone responded differently, and they didn't even look at the results. They used the lie detector simply to keep the employees in line, in the fear of having to face the machine.
This was 20+ years ago, but lie detector technology hasn't changed much.
That is why I am surprised that both the FBI and the CIA use it so frequently, and trust it so much.