TomD
I don't remember him saying he did it to close nasty gaps, his method is built around predictable dovetails at a studio furniture level. I don't consider all the points to be still relevant, and I don't use them all myself, but I did teach the method at one point (I like to teach stuff people can walk out and find a reference for). I do still at times use his file method, and it does close gaps even if he did not promote it as such. Basically you just put a single layer of tape around the end of the file, you leave the endgrain a little proud, and you file it away. I think that just works, I don't think you have to do anything too special, but then maybe I am doing something I don't know, there are natural ways to shift around work to reduce tear-out, etc. The only real problem with this method is that overlength endgrain filed away with a mill bastard file is a little time consuming, but it works.

According to the book he does not recommend making the endgrain long, just a hair, so maybe I have been overdoing it at times, when I did it at all. For everyday work I mark the ends to the thickness of the adjoining piece.