Taking the mechanically driven fan off will improve the fuel consumption slightly. An electric fan that can be switched off uses less power in a lot of conditions.
I don't see why you would have two fans like that. A fan in either position will drive air through both the condenser and the radiator. You could have just one fan that comes on when the engine reaches a certain temperature, or the air con is on. You could leave the fan off above a certain speed even with the air con on, as the car moving will drive enough air through the condenser if you are going fast enough.