"Sennin" wrote:

I have heard that the furnace/AC cleaning is a good idea. I have also
heard that duct cleaning is just a scam, because the filter picks up
the dirt that would be in the duct.

I had my ducts cleaned, but that is because I have had a lot of birds,
and they pulled a lot of debris out of the ducts.

The furnace should be inspected and cleaned every few years at least,
ducts maybe after a couple of decades, they don't get much dust under
normal conditions.