There is fatal risk involved if you let your ducts work for too long without any professional intervention. Even a minor fault can lead to serious troubles. Moreover, lack of professional duct cleaning will lead to more power consumption. Also, bacteria and contaminants will be easily spread across your home/office through the dirty indoor air. In addition to that, you will be required to replace your duct much sooner because it has been found that ducts that are cleaned professionally on regular basis have a long life.