Heater Water Valve??

[slikside]

Hey guys, I have a '72 C-10 with no AC. I know that my heater does not have a control valve on it. I just pulled the whole thing a few weeks ago and haven't got it all back together yet, but I just saw these things in a catalog. I understand the concept (maybe the motor would come up to temp quicker without constantly running fluid through the core), but what other advantage would there be to having one? They have them for AC and no AC trucks.

With my setup (I'm pretty sure it's original) fluid runs through the core continuously. The "heat" control simply operates a diverter on the heater box between the blower fan and the core. Air either enters the cab before or after passing through the heater core. No fluid control valve. Why would you need one for no AC truck?