2.3 heater control valve
 

What purpose does the actual heater control valve serve on these trucks, mine falied so I simply bypassed it with adapters to run it straight in and out of the heater core and my hot/cold settings work as they should.

If it is the valve on one heater hose, then it will stop the flow of warm coolant thru the core inside cab when needed.
Inside the cab there is also a Blend Door that switches air flow, both are operated by the Cold-Hot selector.
In the winter the valve won't do much, in the summer you may want it back as you will notice warmer air than usual, on the vents and near passengers feet.

My '94 has no heat control valve(from factory), heater core always has warm coolant circulating, I never noticed any issue, and maybe you won't either.