The air filter, filters dust particles .. there is an allowable limit as per engine design in microns .. bigger particles act as sand-paper in the cylinder area causing wear .. no local or low quality filters will give u that protection .. u may compare any air filter with genuine one .. the texture and thickness of original filter is visibly different
never use air and oil filter of non oem specifications .. these r the only two filters protecting ur engine from outside impurities .. other than fuel filter which is now seldom cleaned or changed