Myth: Telegrams used STOP in place of punctuation because punctuation cost extra
The real story: Morse code originally had only capital letters and no punctuation. This generally was not much of a problem, but during the first world war when telegrams were widely used in the military, a misunderstood message could be disastrous. The custom arose of using the word STOP between sentences in military telegrams so that any ambiguous phrases would not be misinterpreted. The custom caught on with the public. Even after punctuation was introduced, people continued fashionably using STOP between sentences in telegrams even though they didn't have to.