THANK you (!!) for posting this link. On a whim, decided to look at flight options from Huntsville, AL to Phoenix. (We live in Huntsville, but had booked flights on FF mileage from Nashville, TN -- 100 miles north of us -- to PHX, since as of Thursday night, there were no decent options for Delta flights out of Huntsville that did not stop multiple times in cities where the weather this time of year stinks.) Just for all the local Alabama fans, no doubt, Delta apparently laid in a non-stop HSV-PHX flight of which I was completely unaware until I used your search site. The flight is expensive (!!!) but I was able to transfer from our existing FF/Nashville reservations for a palatable fee. Flights are FAR better overall -- just means we'll be flying back from PHX on Tuesday on a plane loaded with sad, sad Alabama fans.
Short version: The idea is that you buy an airline ticket that has a layover at your actual destination and skip the last leg of the flight. It can sometimes be cheaper. United Airlines and Orbitz both sued because it was costing them money.
Example: Say you want to fly from New York to San Francisco. You book a flight from New York to Portland with a layover in San Francisco and get off there, without bothering to take the last leg of the flight. Sometimes, that can save you money. Flying this way isn't always cheapest, but it often is.