Imagine yourself crawling out of bed at five in the morning to catch a 7 AM trans-continental flight, arriving on the East coast with just minutes to spare before you make the trek back home. At its simplest form, this is a mileage run. Although likely fatigued from the all day journey, tomorrow will be better, particularly since you earned a whopping 6000 miles (or more) for your efforts.
The rules are simple: Fly as far away as you can, for the least possible amount of money. It makes no difference whether you embark off to Sarasota, Florida or Hilton Head, North Carolina, because a true mileage run means you will probably never leave the airport of your arrival city. Just enough time to visit the airport facilities and enjoy a fresh cup o' joe, before boarding begins for your return flight home.
A complicated question asked so many times of me: Why? Why do people do this?
Some view it as a necessity. Frequent travelers who find themselves just a few thousand miles short of maintaining their elite status need to find a way to earn some quick elite-qualifying miles before year end. A mileage run is perfect for them. A simple flight from point A to point B and back allows one to fancy their elite status for yet another year. The banking of useable miles, the ones used to redeem for free award travel, may be less of a priority for this type of mileage runner.
Some regard mileage runs as an opportunity to visit cities while creatively building off-the-beat routings, maximizing mileage potential. For example, San Francisco to Washington D.C is available non-stop, earning 4,820 miles round-trip. Instead, consider San Francisco to Seattle, to Washington D.C, earning 5,956 miles round-trip. For the clever and so-inspired, you could add stops in two other cities enrute to D.C, without adding a substantial cost, to accrue even more miles. These types of mileage runners seek to bank as many useable miles in their frequent flier account, enabling them to redeem for more frequent free trips in the future. (It's important to note that since the focus of the trip is to visit the city - meaning a stay of 1 or more nights is involved, some in the industry do not consider this a true mileage run.)
Finally, a smaller group of travelers view mileage runs as a sort of hobby, sometimes spending hours composing an exciting itnerary that includes four stops - in each direction, including visits to small regional airports that most would simply fly over. These extended mileage runs last upwards of 24 hours, and often include a red-eye flight. The exaustive journey yields huge mileage payouts, and provides avid travelers a chance to see parts of the country - at least the airports, they might not otherwise fly to. Some find themselves volunteering-for compensation on oversold segments, esentially paying for the cost of the mileage run.
But let's face it, if you have an aversion to flying, mileage runs are no friend of yours. But, if you find yourself a bit short of a status level (December 31st is the last day to accrue miles for next year's status), or you want to try your own mileage run, I highly recommend visiting the Flyertalk Mileage Run Forum (it's where I started many years ago), where a community of like-minded flyers can offer expert advice and recommendations on putting together a run that works for you.