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I was told, by someone who knows the fuller story, that the secondary scanner, which is indeed a statistical collection service (so measuring the time from entry gate to reaching the security trays), came about as a result of some challenge from the CAA over a previous, no longer used, statistical collection method. This was one measure of one passenger every 15 minutes. The CAA didn't insist on them but HAL agreed to put them in to assist with the widespread disbelief that the first statistical process engendered.
I tend not to bother. Unless I've been kept waiting.... In which you should do just before slipping through the arch.