Fast Track was designed to let First and Business Class pax avoid waiting with the rabble in economy. Surely the time this is needed most is when it is busy, but this never seems to happen. On many occasions I have seen people moved from the normal queues to Fast Track, apparently to get them through as quickly as possible. Having questioned this protocol in the past, I have since found out that as Fast Track is a free service and anyone can use it. Obviously the best time to use Fast Track is when the Terminals are at their quietest....when you can pick any X-ray you like! (so long as it's manned!)