Well, I had to vote for "They work and slow people down."
Because:
1. They work (i.e. they take photos)
2. They slow people down.
But of course as FTO points out they only slow you down while you're driving over the mag-pad thinees. Hmmm, so perhaps I should have picked the needless braking one.
Still, the advantage of needless braking is the hard accelerating that must follow.
Heh heh hee...