The biggest reason for flying at higher altitudes lies in fuel efficiency. The thin air creates less drag on the aircraft, which means the plane can use less fuel in order to maintain speed. Less wind resistance, more power, less effort, so to speak.

While most long-haul commercial jets prefer the "sweet spot" of 30,000 to 40,000 feet for fuel efficiency, a plane might fly at 24,000 feet for several specific operational reasons. First, this altitude is common for shorter regional flights where the aircraft doesn't have enough time to climb to higher altitudes before needing to descend for landing. Second, pilots may descend to 24,000 feet to avoid severe turbulence or adverse weather conditions like thunderstorms that are more prevalent higher up or to catch more favorable wind speeds. Third, this altitude is often a standard cruising level for turboprop aircraft, which are designed to operate most efficiently in the slightly denser air of the lower atmosphere. Finally, Air Traffic Control (ATC) may assign this specific altitude to maintain safe vertical separation between multiple aircraft on busy "invisible highways" in the sky, especially during congested traffic periods or when a higher altitude is already occupied.