How Home Ventilation Works?
Homes, particularly newer "air tight" ones, need to be maintained in order to remain sanitary and healthy. Ventilation systems (ducts) are no exception.
It may help to understand how home ventilation works:
Simply put, air ducts "breathe in" air through return vents, taking that air to the furnace or air conditioner, then "breathe out" the same air through heat registers after being warmed or cooled. During this process, the air travels through ducts, at which time any number of contaminants can become trapped (or in the case of dust mites- multiply) in the air ducts. The air you breathe must pass over these contaminants before being delivered to your rooms, and ultimately to your family's lungs.
In this way it is true that "if it's in your ducts, it's in your lungs". So, the choice is not really to clean or not to clean the only remaining question should be how and how frequently.