The fuel in the tank gets heated several ways. Ambient temperature, being pressurized and passed through the PPR, the coolant pipes pass right next to the tank. Finally the airflow off of the radiator and condenser. If you have a kinked hose or dirty pick-up filter in the tank and the level is low it is very easy for the fuel to vaporize. And now with all of the alcohol/methanol in modern fuel it is even more prone to vaporize. Anything you can do to reduce this is good to do. There does not seem to be any downside to using the "heat dam". A lot of cars have one and no one has ever reported any ill effects. If you notice problems when the car is very hot or a loud fuel pump a heat dam is a good idea but I would also recommend going inside the tank and inspecting everything to be sure everything is in good condition and properly installed. I also like a spring inside the pick-up hose. When it gets hot it gets soft and that fuel pump can pull a hard enough vacuum to collapse the hose, starving the pump and making it noisy. Once it gets noisy it starts wearing out prematurely.
David Teitelbaum