I don't like publicly defending poor danial. But wth. It is filing a saw, I do the same thing, except I sit on the saw. I understand the comment about the chaps, its a safety thing. But back dragging a file??????? The true safety concern with his filing is he is pulling the chain back toward himself, if he were to slip he could cut the hands he uses for teaching. I tell you what, next time you cut a limb off a tree with you hand saw take it out of the wood on each push stroke, it dulls the blade.
No not really, watch it though, on your push stroke the saw dust that was stuck in the teeth comes out (at least some of it). File is the same way, except it is designed to cut steal.
Swingingdude is right about counting teath, if you want to waste chain file to that worst tooth, its your money. But I bet money that my saw with odd teath will cut just as good.
Ducking now.