I have been told that my cold air returns should be up by the ceiling instead of down in the base board area of my wall. I need to know if there is any truth to this and if there is what are the benefits to doing this. I am having a new furnace and air conditioning unit installed and the contractor can do this for me if I choose to have their recommended changes made. I am just wanting to do what is necessary to optimise my purchase.

That contractor should be capable of evaluating your homes duct system. If you heat way more than cool like we folks in the midwest, your returns should be near the ceiling.

The return at the ceiling is a newer accommodation for air conditioning. Many cool air returns just use the wall cavity as a duct from the floor up. You can have a vent top and bottom just for the price of the grills. Close the one at the top in the heating season allowing the cold air to flow into the one at the bottom. In the cooling season, open the top and close the bottom allowing the warmer air at the ceiling to return