He is saying not to bother with controlling the pump with the controller, just use the dial on the pump.
I do somewhat agree with that. But the heat dump of the pump's controller is a good point I think.
The pump undervolts the 12V power. That means if it wants 8V speed, it will burn away 4V, turning it into heat, which will be dumped into your loop.
But if you use the CW, the undervolting is done in the controller, not in the pump. So no getting the water warmer this way.
And it's a mystery wrapped in an enigma to me, but the CW can undervolt without creating any significant heat.