A fuel filter is just that a filter that filter's out the debris in the fuel that you put in your car. What happens is the debris starts to plug your fuel filter and then less fuel gets through. Now in a perfect world the fuel would be clean and you would not need this, but that's not reality unfortunately. Vehicles who have a serviceable fuel filter we recommend that they be replaced every 15,000 miles. For those that are not serviceable don't worry about it.