A few years back, it was popular to add a pressure tank or surge tank to the fresh water systems of RV's. The purpose was to have a small reservoir of water available to draw from without the on board...
I had accumulator tanks on my boats. They do cut down on pump noise & supposedly extend pump life but I have never put one in the 5er & we draw water from our own tank exclusively. Thousands of gallons have gone through the pump & it is still going strong. The noise is not bothersome at all to us. In fact it is beneficial, letting us know if a tap has not been turned off properly or if there is a leak.