I laughed when I read it, because my father-in-law just finished telling me the same story about a dishwasher he installed in a new house he built in the 90s. Water everywhere the first time it went to drain. He was perplexed until a friend asked him if he drilled out the plug in the p-trap.

Of COURSE you can't just have a hole in the side of a pipe under your sink, but the existence of the fitting gives you a false sense of security that it's plug-and-play.