Originally Posted by BubbleheadMd
No, it's to achieve a totally smooth surface with no microscopic crevices that will allow crevice corrosion to take hold.
Stainless steel does not rust on the surfaces exposed to oxygen, but they do corrode and fail in an anaerobic environment, which is usually the part of the chainplate that is encased in the deck.
Polishing is not the same as ELECTROpolishing. The former merely makes the metal shiny and pretty. The latter is an electrical acid bath process that removes the iron molecules from a thin layer of the surface. This gives corrosion no place to start.
If you want nice, shiny AND corrosion proof chains, first get them cut, drilled & ground to final shape. Next, sand them and polish/buff with a wheel polisher. When they look like you want them, have them electropolished. When you get them back they will no longer have the perfect, shiny finish but a SMALL amount of buffing will bring it back.
You have to be careful with this last step as the protective layer is apparently only .001" to .0015" so you can buff right through it if you go to heavy on the final buffing.
I did mine this way years ago and they still look like they were just buffed.