In general, the idea is you'll save gas by using the turbo more at very low RPM's then revving the engine. When I ran trucks, the International's all had an "Economy" button on them which told the Allison 5-spd Auto to shift sooner and use the turbo. The only down side I saw was that out of a fleet of 160 units, I replaced probably 10 turbos within 2 years. Keep in mind however, this may have had nothing to do w/ the shift patterns and more do do w/ the fact that they were heavy duty long distance haulers.
At any rate, I don't think you have anything to worry about. It's your computer shifting for fuel economy.