I have a good friend who worked as a strip sawyer when we had such things, he filled his saw that way either square or round filing looks weird but sure worked for him.I called my logger buddy and asked him how many sharp, spare chains he carries to the job site in his truck when dropping big trees with his MS 660. Andy said, "Usually five or more. You would not believe what I run into when cutting 36" dia. cottonwood."
Andy is right handed and file sharpens his chains with the bar attached to the saw and resting over his left shoulder.
Exactly, I keep just touching the chain up till it wore out, hit the rakers occasionally couple passes will do it. I take more saws then I do chain, never know when you may need another saw. I put the chain on my saw once and it stays till its worn out.