We had a 460 with carburetor and the A/C compressor was a two-cylinder York, which is very horsepower-intensive. On a setup like that it would make sense to run "house" air instead of "dash" air. We tried that, but the heat from windshield and engine compartment didn't make "house air" very satisfying.
A V10 uses a very efficient axial or possibly scroll compressor. Also, unlike 460, is pretty much immune from overheating. So: I do what makes me feel good. Either, Neither or Both. The fact the chassis gets 7-mpg is the factor, not the A/C on/off question