Engines require a mixture of air and fuel to start and run, and this air carries debris with it (dust, dirt, road debris etc.). This filter is responsible for trapping this debris so that only clean air enters the engine.
When an engine ingests dirty air, some of the debris will find its way into the engine’s lubrication system. If debris is run through the engine bearings, these bearings can develop wear that results in internal engine failure.
Engines with mass-airflow sensors may not run correctly (or at all) if debris collects on or contacts the mass airflow sensor.
Removal is often simple for these filters. However, certain designs will require removing or taking loose the air intake tube. Occasionally, debris should be blown out or removed from the filter housing.