It's true, but your top speed will reduce. It's almost like changing gear ratios. More importantly, at any given speed in a particular gear, your RPM's will be higher. Will probably waste more gas because of the RPM's going higher. Spedometer error will be introduced, along with who knows if it will cause issues with speed sensors and such (ABS, ESP or BAS). Don't know if those can be corrected by programming.
Not worth it, IMHO.