Depends on your driving style. If you get a remap and drive everywhere with your foot to the floor it will get worse.
At the end of the day you need to burn the fuel to generate the power, more power = more fuel - up to a point. The optimum AFR for max power is 12.5-12.7 but cruising you might be up around 17 or 18 for instance. BUT it can also mean using less fuel around the cruising areas of the RPM range, so you may notice a slight improvement on long journeys, but a definate decrease on shorter ones.