Post installment cleaning:

After being installed most the times dust and dirt and some plastic wraps or tape might be le
in the ducts, with time it will collect more dust, bacteria and mold, causing the whole thing to
be less efficient and producing less clean air.
Sanitizing and killing molds and bacteria:
An uncleaned duct and AC no matter how clean the external filters are is still vulnerable to
bacteria and molds, with time produced gases that the duct is dealing with is going to end you
up with these infections, an infected duct will put your health in danger and even your
inventory specially food since mold is air born.

Treating insulators:

Insulators have a life span, if exceed black spots would start to show at the air flow vents, that
will travel through the air as black dirt particles causing breathing issues and infections.

Efficiency:

Maintaining your ducts and central AC clean means less high cost repairs, less electricity
consumptions and a longer life span to the filter, insulation and over all your AC unit.