I use mine for a couple of things. When setting the cruise control on an open highway its useful for picking an efficient cruise speed. I think this is probably the main purpose especially on roads like the autobahn where you have to make decisions to cruise at 100mph or perhaps 130mph. Aircraft POH's have charts for deciding cruise speed vs engine fuel consumption. On a high speed long distance trip it could be the difference in stopping for gas and not stopping for gas. One of the 140's strong points is its incredible range.

Its also quite useful for determining if the road you are on has an upward slant or downward slant. If you notice the MPG dropping your going up an incline and the cruise is throttling up to compensate and if you all of a sudden have great fuel economy your likely on a slight downward incline.