A clean fuel filter is important to keep an engine running smoothly. It does so by ensuring contaminates don’t pass from the fuel tank into the extremely narrow passageways found elsewhere in the fuel system. A clogged fuel filter will starve the engine for fuel, resulting in sputtering and loss of power, and can cause stress on the fuel pump. Generally a fuel filter should be changed every 50k miles. Older cars with corroding/rusting metal fuel tanks may require more frequent changes, which is often an easy DIY task.