I’ve wondered this. I think it does matter a little, because the sun coming through the windows, and beating down on the roof, an the hot air that seeps in through cracks in the house are part of the equation. I know in the winter if I turn my heat way down it makes a significant difference in my bill. Air from a setting of 77 or 78 might not make a huge difference, but probably a setting of 72 vs. 78 is noticeable.