I've a friend who's a trouble shooter for a multinational. She's dedicating the next year to get 1 million frequent flyer miles which she should get quite soon. We asked why it was so important, and she said, that 1 million miles will get you priority boarding for life. If you don't get priority boarding, you won't get a seat near the front, and you won't have space for your hand luggage. If you don't get those, you won't be one of the first off the plane. If you're not one of the first off the plane, you might not get a space on the first bus to the rental car hire. If you miss the bus, you have to wait 20 mins, and by the time you the bus delivers you to the rental car hire, the queue could be an hour. It's all a giant knock on effect that could mean that rather than take 20 mins to finally get out of the airport, it could be 2 to 3 hrs.