when to use "econo mode" on Allison 5 speed tranny?

It is supposed to hold the gear longer to prevent constant hunting between 5th and 6th gear when highway driving on rolling hills and flat roads. Doesn't do anything for city or mountain driving. More or less holds the gear a little longer so it doesn't shift as often between the higher gears.
I don't use it because it seems not to make a difference on my coach and it doesn't change my mileage