What is the purpose of using potato peels for seasoning a cast iron pan?
I personally had never heard of it, but after doing some research online, I found another set of instructions that called for boiling potatoes in the pan before seasoning:


  After boiling potato peelings for 15
  minutes, the skillet had a nasty
  slurry of grey looking sand in the
  bottom  Once the skillet was heated,
  the pores were opened, and the
  starchy/water mixture was able to draw
  out oils and dirt that I was not
  capable of getting to through normal
  washing. I fully do not understand the
  science behind why the starch/water
  mixture did this, but the experience
  was enough to convince me of the need
  to do this. So much in fact, that I
  did this process twice on each
  skillet.


I read a few too many web pages while researching this, and didn't save all of the links, but I did notice a few things:


Some of the posts kept switching between saying cast iron and carbon steel; both are typically seasoned, but they're different materials, so I don't know if it's recommended for both, or if people were mixing things up.  (I only have one carbon steel item, a wok, which I got second hand, so had already had its first seasoning).
Some of the posts mentioned boiling potatoes for 15 minutes, other mentioned frying potatoes as the first thing to be cooked in the pan (in oil), some mentioned cooking them 'til they burn.  The boiling potatoes ones also mentioned it works for cleaning stainless steel pans.
Some mentioned peels specifically, others say that you can use any part of the potato ... if it's the starch that's of interest, I'd think the middle would actually be better, but I'm guessing that the peels were considered waste, and so considered a less valuable item; I'd be inclined to just use one potato, dispatched with a peeler, if you were trying to avoid wasting potatoes you weren't going to eat.