shellac on steel bodied hand planes

I was wondering what is the reason for putting shellac on steel bodied hand planes, is it just to protect the Japanning or is there more to it or a different reason all together? I was also wondering how long it lasts under normal use-I don’t want to be reapplying it every month. I have always just waxed mine but have recently seen a few different blogs that have talked about this but not the reason why. I have a Stanley #4 that was not taken care of that I picked up at a garage sale for fifty cents, after a lot of elbow grease it works like a champ, but most of the Japanning is gone. I came across a site that I am providing the link for below as I was researching before I bought my #78, and if the job was done better (he states that he did a quick job and was going to redo it later anyway) I think it would look pretty cool. With the Japanning gone on this plane anyway it would be a good experiment plus I have another #4 that the Japanning is about 90% plus it has a lot of sentemental value as well. I like the bronze look that the shellac gives, to me it looks pretty classy. Any info or heads up would be great. Here is the link I was talking about that shows the coloring on the steel- http://www.inthewoodshop.org/methods/stanley78/10.jpg
Thanks so much for all the help you guys and gals.
Nate