Guess what? Dirty filters actually filter better than clean filters. Then, at some point there becomes an undesirable amount of restriction.
For high value engines and equipment, filter restriction monitors/indicators/gauges are used to optimize filter life and protect the equipment. For ours cars, wouldn't you think, with all of the sensors on the thing that if filter restriction was so critical there should be some "P0blahblahblah" code or a light or something to let you know to change the filter? Nope. Just basic guidance of change it every 15k,30k (whatever) miles or months and a service tech keen eyeball (gimme a break!) of how many bugs are laying on the filter surface. There are so many variables to each particular car's environment.
Change the filter at recommended interval to protect your warranty and don't sweat a lil' dirt