I've never understood the value of this option. It is only useful if you can predict, a year ahead of time, exactly how many miles you'll end up with. If you undershoot the target by more than 5K miles, or if you overshoot the target by even 1 mile, then it's useless -- you have to land in exactly a 5K window for it to have any value.

Perhaps others can predict this level of accuracy a full year in advance, but the way it works right now, it seems totally useless to me.