I believe he sharpened a variety of hooks, both coated and un-coated.
He also said that, almost all of the time after every fish the hook needed to be changed. However, if you were fishing on a one fish a year water this would obviously be worth it, to hook the fish of a lifetime.
If he does not catch, and brings in the hook after a days fishing, he 'touches up' the hook, with the file to restore it to sharpness.
You say about the point being brittle, surely if the hook is sharper it will penetrate further, meaning that the point will have less pressure on it, due to the hook being in further.