Due to its widespread use as filler text for layouts, non-readability is of great importance: human perception is tuned to recognize certain patterns and repetitions in texts.
If the distribution of letters and 'words' is random, the reader will not be distracted from making a neutral judgement on the visual impact
Furthermore, it is advantageous when the dummy text is relatively realistic so that the layout impression of the final publication is not compromised.
The most well-known dummy text is the 'Lorem Ipsum', which is said to have originated in the 16th century. Lorem Ipsum is composed in a pseudo-Latin language which more or less corresponds to 'proper' Latin.