When racing does folding the mirrors do anything?

I know maybe this is a silly question, however, in the case of the ford excursion just for having the towing mirrors vs the regular highway mpg decreases by about 2 miles per gallon. I cant imagen there would be a noticeable difference folding in your mirrors, but would there be one is the question, and would it be helpfull or harmfull?

Read more: When racing does folding the mirrors do anything?