Its legit.

Sharp edges in the combustion chamber are a no-no since they can create hot spots that can cause pre-ignition.

One of the things they used to have me do at the speed shop when I was a kid was file, sandpaper and beadblast the plugs that went in the higher compression race motors.

The other hot tip is to slightly bevel the edge of the electrode and plug body too.

The rule is no sharp edges since they will become the hottest spot in the cylinder.

If you really want to be anal about your plugs, you should also index them so they do not impede the path of the flame front.