Your ductwork is used with every traditional central air conditioning and heating system that in America. Meaning if you have a furnace in the closet, attic or basement, you have ductwork.
Why Its Important To Your Comfort
Without the right sized duct going into each room, you will have uneven air temperatures in your home, hot and cold spots. Long run times or even worse short run times of your HVAC equipment which can damage your furnace or air conditioning equipment. Not having the right size return air (ductwork that sucks into the furnace) can damage your equipment, lose efficiency, and not perform the way it was intended to.
Not having your ductwork installed correctly can cost you not just money but in comfort too. Many studies found that not having it done correctly can drastically reduce efficiency and waste energy. The most common problems are air leaks at the joints and at the ceiling where it connects to the vents.