And it's not just the gain in fuel economy in the higher levels. The fact is that a jet engine is quite unlike a piston in that your descent can be at flight idle the whole way back down - if you've worked out your profile just right! This helps to save even more fuel, which translates to a lower cost for the operation and, therefore, more profit to apply to the days when you need to go missed approach of an ILS!
Besides, as
j_t says, there's the added incentive of not being the one to buy the first round of drinks!
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Dispela olgeta samting i pekpek bilong bulmakau!