PKs go a long way in educating the distributors, contractors and architects who are always anxious for knowledge. They educate the “educators” who, in turn, are forced to extend and inform themselves rather than look foolish when doing a PK of their own.
PKs on ceramic tile are not usually done. Most people just believe that ceramic tile is ceramic tile is ceramic tile. Most end users are unaware of the differences between, for instance, a glazed wall and a glazed floor tile.