On my last trip flew to and from San Jose, Costa Rica on planes that had huge sections unused due to pricing. The rear section of the plane was sold out. The center section was nearly empty. We were told if we wanted to move, That section was premium economy and we would have to pay a steep three digit upcharge fee, Even after the plane was in the air the fee remained. How does it make any sense to fly a plane 4 hours with nearly a third of the seats unsold and unused. The "premium" seats were not any wider, the free movies were the same, the pretzels and services were the same. Probably had more leg room.