The most informative air filter document that I know of is “Nanofibers in Filtration Applications in Transportation” by Employees of Donaldson Company given in 2001. Here is a quote about consumers and light duty vehicles:
“Consumers must also make maintenance decisions about the air filters in their cars. This user group is relatively unsophisticated in their knowledge of filter maintenance and function. Air filters are perhaps the most easily serviced but least understood part on a vehicle. Other common replacement parts on a vehicle such as tires, wiper blades, oil and oil filters work best when new. However, this is NOT the case with conventional air filters. Since most (dry) air filters rely on the formation of a dust cake to improve the performance of a filter media, over-servicing can lead to dire consequences from inadequate engine protection.
Over-servicing is common in light vehicles. Light vehicles are generally not equipped with filter restriction indicators. Air filters are often inspected by maintenance personnel during oil changes. In spite of the typical manufacturer's recommendation of at least a 30,000-mile change interval, it is common for dealers and quick lubes to recommend more frequent air filter changes. Given the frequency of oil changes and air filter changes at quick lubes, it is expected that many light vehicle filters are changed much more frequently than manufacturers recommend.
While this over-servicing phenomenon is frustrating to those who understand filter media performance, the filter industry has not sufficiently educated customers on how air filters function. Not surprisingly, filter manufacturers, distributors, dealers, service stations and quick lubes have economic incentives to change and sell more filters. It is also understandable that consumers believe that filters work best when they are new (like other parts) and have a clean appearance.
In spite of the best intentions of automotive mechanics and consumers, typical automotive air filters are notably inefficient at capturing particles less than 5 microns in size. Several studies have shown that particles between 1-5 microns cause engine wear, which will lead to increased engine emissions and shorter engine life. Because many car engine air filters are over-serviced, a typical automotive filter may operate most of its life without the protective benefits of a well developed protective dust cake. As the filter becomes dirty by visual appearance (and the dust cake finally starts working) the filter is often exchanged.”