The partial burning of fuel is eliminated providing the maximum energy release available. This energy is not all available for motion uses since the mechanics of the engine involved are never 100% efficient.
However provided that aggressive use of the extra energy is not enacted, it will be translated into lower consumption of fuel for any given movement.
Lastly the amount of fuel consumed for any given distance traveled is directly linked to the amount of CO2 your engine emits over any given distance.
in other words the more MPG you get the less CO2 per mile you emit.
To give you an idea of how much you could save it is worth knowing that one litre of diesel will produce 2.64 Kg of CO2.