The only purpose I see is to regulate the flow of water in the system. A ball valve could be used for the same purpose but it would be missing the test ports and the % gage on the top of the valve. It the pump can pump 10 gallons a minute and the coil is rated for 5 GPM at 140 degrees to get a 60K BTU output then the valve with the blue handle can give you the proper flow rate with the ability to measure your flow.