Mainly for you to create a controlled environment where you're not running the turbine at 50K and you're not taking anything out of the jet. It should help determine if the pump is actually delivering fuel properly. Example, when you increase the throttle the ECU is telling the pump to flow more fuel. In a closed loop you can test this manually, you can set to a desired rate (up or down) and see what is happening (flow wise). More importantly, you're taking a lot of variables out of the picture. If it works perfectly and you are able to run it at a high rate/flow, then you can begin to suspect other aspects of the system. I think there are small gears that mesh very closely in the pump, even very small foreign bodies can easily jam the mechanism. If it sat,it could be gummed up. Running the pump for a little while might help clear it out. I'm just speculating here, having the jet would make diagnosing things much easier. Just trying to help.