Working a single frequent flyer program can really pay off. Airlines send you regular first-class upgrades after you've flown 10,000 miles. The higher your mileage, the greater your priority in receiving these special services. This can come in handy if you need to change planes or your flight gets canceled. The airlines take care of their best customers first.
Airlines always board their first-class cabins and frequent flyer passengers first.
This means I can snag some of that precious overhead bin space. When you're trying to fly into a city and still make some appointments that day, carry-on is the only way to go. It can save up to an hour of time. Speaking of bins, let me go off on a rant here. I'm very supportive of the airlines finally cracking down on carry-on luggage.