It's more efficient than a low flying aircraft, due to reduced drag from ground effect. But it's not more efficient than a high flying airplane getting reduced

It's more efficient than a low flying aircraft, due to reduced drag from ground effect. But it's not more efficient than a high flying airplane getting reduced drag from lower air density. So it works on short distances where the airplane would use a lot of fuel to get to high altitude, but on longer distances it wouldn't be more efficient.