I've never seen it happen and I would think the only reasonable justification would be if the passenger is very pressed for time indeed. I've once seen one machine open and a queue back to the BP check - but even then the queue moved pretty quickly.

So - maybe VIPs? I don't see why VIPs should be getting special treatment unless for justified security reasons but I'd hardly see TFW as a particularly risky place.
Anyway, what makes VIPs in the first place? Who decides?? Celebrities? Give me a break. MPs? Certainly not. Cabinet ministers? Also not. Maybe foreign dignitaries to show hospitality and politeness - but I kind of assumed they went through another channel and had a Jaguar to the plane?

Maybe full fare F tickets? I think anyone paying full F might deserve it!