In criminal case, polygraphs are tools used to obtain confessions. For example, the device itself inspires fear so an examiner may ask a series of background questions before the test commences in order to establish a baseline that are tantamount to criminal confessions. Also, the "deception indicated" information results in follow on questions that again result in confessions from those who don't understand they can tell the examiner to get lost as the device is reading wrong.
In administrative/civil procedures, polygraphs can be used to initiate adverse actions. Polygraph results are 60% to 80% accurate, so are of some value. Law enforcement agencies also tend to argue the results are more accurate than the opponents claim they are.
The polygraph results may be admissible in some jurisdictions under certain circumstances.