Originally Posted by
WillCAD
They serve one moderately useful purpose, though it's not a security measure per se - they are meant to limit admittance to the sterile area to ticketed passengers only, which reduces the number of people screened, which shortens lines.
Even with pre-9/11 screening, limiting sterile area access to ticketed pax only significantly reduces the number of people clogging up the screening checkpoints. In the old days, it was common to see whole families seeing off grandma and grandpa on their trips to Boca, or Junior on his way to college. Now, only the travelers themselves (with a few limited exceptions) pass through the c/p, and the lines are still unwieldy - imagine if the BP check was eliminated and travelers could bring their entire entourages with them.
So although I know that the ID check does nothing for security, it does prevent people from printing a dozen BPs on their home printers and bringing the whole clan to the gate to see them off.
Most European airports I've been to do only a BP check, usually by scanning the BP electronically, using automatic gates. It works well enough.
If really necessary, it wouldn't be hard to implement a system that only lets a passenger through once, with manual intervention for going through again (since there are some legitimate cases where that could happen). You'd still need to have one person manning a group of automated gates, but that's better than 6 ID checkers for the same throughput.