As the fuel filter clogs it not only restricts flow but can also cause erratic flow. Some folks claim a performance increase after replacing a very dirty filter. I think it's simply a matter of restoring normal flow and eliminating some erratic engine behavior. But that's only in severe cases, IMO. It's probably a good practice to replace your fuel filter on these engines every 30k miles or so but I know many people that change fuel filters every 60k or even 100k miles. It depends on the fuel in your area and how much crud comes off your tank, fuel lines, etc.. Replacement is cheap insurance. The filters are less than $10 at most auto parts stores and not too hard to replace yourself.