Not sure how good they are but they are used for a lot of folks in sensitive areas...”regular” TS/SCI doesn’t require one but when one gets into positions where the data becomes more critical require polygraphs.....in my years as a Security manager, I never heard of a specific individual failing one and being denied the position but have heard from a couple that they caused some “spikes” which resulted in additional interview time to try to determine if there was a real issue - who knows if they serve their purpose....some folks can beat them w/o problem and other give false positives...perhaps the majority can be fairly well vetted but nothing is perfect and individuals can make the decisions......
“TS/SCI doesn’t require one but when one”
While in a TS career, DH would be polygraphed at random times. Maybe it was done in conjunction with a specific program he was working on at the time; I’m not sure. I can’t remember.