Through chiptuning you will get more power from the engine. This means that your engine has to work less hard for the same result. For diesel engines a saving between 5 and 15% is feasible. For gasoline engines this is a bit lower and up to 5% is achievable. Please note, however, that these figures are never guaranteed, since there are several factors that influence this margin. Think of driving behavior, whether you mainly drive on highways or in built-up areas, how heavily loaded the car is, etc.