Don’t think of your carpet as the bad guy, it works as a filter. Your carpet collects the dust around you by trapping them below the pad where you won’t be troubled by breathing them in. Of coarse every hero has a side kick and so your carpet too needs help every now and then. Therefore regular vacuuming and cleaning helps remove the small dust particles from fibers on the top. Pay close attention to the edges around your walls because dirt collects there and when your cooling cycle is on, it often pulls greasy dirt to that area. That is why you get those black lines on the edges of your carpet. They are called filtration lines. Chem dry has a process which removes most of the filtration lines if not all.
Even if you clean your carpets regularly, meticulously remove dirt and other allergens that help extend life of your carpet but if you want to help your family breathe easier you should consider Professional cleaning every six months to a year. It is much cheaper than replacing your carpet every 8 to 10 years.