MWAA (IAD airport authority) uses them for the standard (non-Pre) checkpoint at IAD before people head downstairs and then again before they enter a premium line. At Pre-Check, the contractors confirm a Pre-Check symbol on a BP

The question isn't whether a given individual "needs" the extra nanosecond interruption, it's whether there are enough people who wind up in the wrong place and cause a disruption that it's worth paying someone to screen the morons out.

People flashing GE cards, itineraries but no BP and whatever else they've got are better dealt with before they get to a TSA podium and an Officer. Even if they get the boot, it disrupts the line .

I'll take the nanosecond over the time it takes to have the line disrupted. I find that if I've got my BP up on my phone with my BP showing the Pre-Check symbol, I can slow down and barely stop at the entry point.