It’s a fact that the air in your house is not 100% clean. There are many floating particles constantly filling the air besides dust, polen, dander and mold spores. All of them risky and dangerous for your health. 

Breathing quality air at home or office is very important to avoid allergies and asthma and for that reason you have to be sure that all ducts are properly maintained. 

Changing air filters often is not enough for a very simple reason: those small particles remain all along the ducts going back to the house every time your AC/Heater starts.