Jim, I've left them because I believe the CSV is building back pressure on the pump by preventing the tank from getting above the pressure switch cutout point. Those relief valves are set pretty high and I'm concerned that if I remove or plug one, I'll come close to deadheading the pump and cause big problems. If the guy responsible for the well says it's OK to remove it or put it further down the line, I'll do it but I want him to be responsible for any damage, not me. They would be easy to plug or remove, I'm just not willing to risk it. I'd rather deal with some water than the fallout of a dead pump, especially since all of my well systems are on residential properties where the well is also supplying the house water.
I think of it like the air inlet valve for a PVB, if it's venting water, there's probably a good reason for it and you probably want it to be able to do so.