I understand that 4" xx slim files are appropriate for filing certain tooth size. It is obvious that a 6" std file will leave a lot of unused file if you use it on small teeth. It is also obvious that an eight point crosscut handsaw teeth can't be shaped and sharpened with the 4" xx slim file.
My question is, what is the reason for the small file size other than conservation of your files. The small file sizes are not readily available. Since the file is triangular at 60 degrees, you can stop filing when your saw teeth are appropriately shaped and sharp.
With the issues concerning saw file availability, we pretty much have to buy what is available.
I just re-toothed a 14 tpi crosscut saw successfully with a 6" slim file. Inquiring minds want to know.