Polishing components contain small amount of abrasives to "polish off" irregular surfaces. Unless there is a clear coat paint (like the current cars), I doubt there is any positive effect by polishing the unpainted surface of MBP's exteriors. With the clear coat paint, you can polish off the ridges on the paint surface to make it smooth. But, with unpainted surface such as MBP's, there is nothing to polish off, unless, of course, you are talking about the heavy duty polishing compounds which scrape off the actual metal surface😱 .
If you insist on the exterior care of the MBP, maybe a canauba wax or synthetic wax would be a better choice (I am kidding). I suggest P21S, Souvarant (I may have misspelled it), and other high end wax/sealant.
