This is MY experience. I was running a valve, The motor was getting hot from what I believe were pockets of air. Adjusting the valve was no help. I then opened the valve all the way and used a wire tie to keep it there. I then tapped into the intake manifold and installed a pressure relief valve. I vented it thru transom and adjusted it to 12 psi. No more problems. On a side note I am running the Rex Marine thermostat bypass.
Some folks say if you run a valve you run the risk of filling your block with sand. It's supposed to be because there is not enough pressure to flush it out. I personally don't "get on it" in shallow water.