The characters ask a question you would have thought they'd have asked long ago; they're asking it now so the audience can hear.
Eg, Agents Malone and Fitzgerald are getting out of their car at the missing soldier's house. Fitzgerald asks, "Since when do the army use the FBI?"
One wonders, why didn't he ask that back at the office when they first got this assignment, or during the car ride? Because we wouldn't have heard it then, that's why.
Used to combat Fridge Logic
. Likely to prompt an En Route Sum-Up
. An alternative to Tell Me Again