then there should be at most 3-5 seconds left. You get 20 or more seconds and you'd want your offense to still at least try to get into position to take a shot or two at the end zone and then settle for a FG after getting a completion or two. No way you settle for 3 when there's still enough time to possibly get 7.
That's why it's so unique. There's gotta be less than 10 seconds left at the time of the punt for an HC to even think about it.