A key thing with files is understanding that they are consumable - a lot of guys don't get this, and continue to drag a file across cutters, long after it stops cutting effectively.
A good comparison is with sandpaper - once it stops sanding, it does not sand 'finer', it just stops sanding, and it is time to replace it. That said, some sandpaper lasts longer than others; some sands faster, but wear out faster; some leaves a finer or coarser surface; etc. Buying round files a dozen or so at a time really drops the price down. especially when on sale.
Keep 'em clean with a file card; protect the hardened edges from chipping/banging against other files when not in use (soda straw, wrap in paper or rag, etc.); toss them in the recycling bin when dull.
Philbert