I've never been polygraphed and I have conflicting views on it, but I suspect if I were ever in the same situation I'd do the same thing. They may not work perfectly, but they are a forcing function to the interviewee. Are you going to tell the whole truth in all its messy detail or not?
That said, I don't think they belong in the justice system. Someone who is already accused of a crime has to choose between either doing a polygraph and being potentially being nervous because their freedom is at stake, or denying the polygraph and looking guilty.
But like you said, in a legal proceeding they are terrible to use.
“We took a privately administered test by a certified polygraph administrator and my client passed with flying colors!!!”
Agree, and also agree, it's insane. Still that's the presumed thinking behind it.
The (anti-polygraph-myth) site I linked comes to a similar conclusion.
If you're just as nervous during control questions as lies then it would be a false negative. The "tack in shoe" tactic is supposed to make yourself uncomfortable during control questions by stepping on the tack and raising the baseline.
It is insane it's still being used in the US.