Air filters sift out particles while a car takes in air to keep these particles and dirt out of the engine, where damage can occur. Keeping an air filter clean and unclogged helps the car's long-term well being.
An engine must work harder than normal when the air filter is clogged. If the engine has to constantly breathe, a clogged filter constricts the flow of air, affecting acceleration and general handling. The car will feel sluggish while driving, and increased wear and tear increases the chances of a breakdown.
Having no filter at all is potentially worse than using a clogged one. An air filter acts as a barrier between dirt and the engine. Without that barrier, dirt can gum up the engine, causing it to seize up completely and leaving it ruined.
An air filter should be swapped out every couple of oil changes or, more exactly, 8,000 miles. If the filter was defective or damaged and dirt has made it into the engine, a flush is recommended; leaving inner workings dirty, even with a new air filter on, will still affect the vehicle's performance.
