Forward vs. drag filing action comparison - video

[Toolmaker51]

I don't and won't drag files, regardless results of automated test.
People don't push in direct reciprocation, equally consistent pressure, or parallel to the file itself. Proper filing angles just less or more than angle of the teeth, partly reason file widths and lengths vary. The only file regularly used 'square' is the lathe file, which has severely (in comparison) angled teeth and safe edges to not alter corners
I separate files for brass from those for other materials.
Like Frank S, knocked down surfaces that wouldn't seal before, not engines, but various industrial pump faces. No choice when it won't fit a machine, or on location.
The better and selected files are stored not in contact with each other, and will chamfer a corner that passes for being hand sanded 250 grit or better. That kind of work was common in tool work, molds, dies, fixtures, prototypes etc.
Long files have a better working life because the wear is distributed over greater area.

The 'system' of filing as taught by Swiss, German and Belgian (3 most prevalent) is how I started, and still use; having 95% of the files I started with.