This simple barrier of accordion-folded paper may look insignificant but it's responsible for providing clean air to your vehicle's cylinders. This is important because air is just as crucial as fuel in the combustion process that powers the engine. Air is drawn through the engine air filter, then the air intake manifold and into the cylinders. There, it mixes with fuel to create the small explosions that power your vehicle.
A dirty engine air filter can prevent the cylinders from drawing in enough air, which throws off the fuel/air mix. This can result in poor fuel economy.