Nuts are almost never perfected at the factory. Maybe the notes run a tiny bit sharp at the first fret, or an open string is a bit muted. A couple of light swipes with a properly sized nut file and perfection is found. When replacing a low quality or worn out nut, a nut file is essential to the job.
Hosco nut files leave a round-bottom groove, so tuning is more stable when bending or using a vibrato. The aluminum case is both a handle for the nut file, helping to keep it straight and giving a better hold as well as a storage case for the file set when not in use (though I also keep the kit in the plastic screw tube it came in for extra safe keeping). These files are much more precise and easier to use than welder's files.
I am satisfied with these files, and don't know how I got by without them.