Red eye last night LAX-JFK. The captain announced that due to storms over Chicago, he was going to shift course and, as a result, the flight would (and did) arrive 45 minutes early. This means the regular route is intentionally slow. Query whether that is (i) for fuel efficiency, (ii) due to allocation of landing slots & gates at JFK, (iii) because the flight is more popular if people can get more sleep or (iv) other.