Originally Posted by DL-Don

In the days of Medallion and Royal Medallion, a Medallion could buy an upgrade certificate for one-way (not one segment) for 1500 miles. You then received double miles based on flying First Class. So even the shortest trip going through a hub earned 4000 miles (2000 in each direction). When you spent 3000 on 2 upgrade certificates you then earned an extra 4000 miles for being in 1st. Subtracting the 3000 spent on the upgrade certicate you still came out 1000 miles ahead compared to flying coach. Of course, on cross-country flights, it was even more profitable.