If you hold a big knife with a mirror finish just the right way, you can see your chin while you shave it with said knife, thus avoiding the infamous bush shaving accidents so prevalent among the lumbersexuals who feel the need to remain perfectly coifed during a life changing overnight solo expedition in the Muskoka's to find their inner man. Me, I sometimes forget to change my underwear for a week or two, and find the mirror finish helpful when cutting them off in the dark after the freeze dried chilli experiment ended badly.
I pick mirror finish!