well, the barefoot herbalist says it best but i can attest that keeping my feet out of socks and shoes has definitely made me healthier and warmer. and yes, when we had snow i checked the mail in bare feet. i dont think anything of it except maybe to think about how good it is for me.
the feet are to be bare and on the ground in nature. by the way, my feet never feel cold and many times are quite warm indoors. i cant stand anything on my feet.
there is more to it of course, like stimulating lymph and the feet being a second set of kidneys. the mud on the ground absorb the salts and the feet stay clean and odor free. put them in socks and shoes and not so much.