A stock intake manifold needs some heat all of the time. It benefits from more heat during startup and until the engine reaches operating temperature. That transition is the job of the original flapper inside of the box.
Heating the intake with water is only good for providing the correct amount of heat to the intake manifold once the engine has reached operating temperature, which means that it isn't exactly useless, just not practical in you want to hop in the truck and go with a cold engine.
