> Well, for example NUL, "start of heading", "start of text", "end of text", "end of transmission", and all the other now meaningless ones
When ASCII was developed, those were far from meaningless codes. They allowed ASCII to be utilized as an "interchange" format (the word associated with the final I in ASCII) between systems (i.e., the communications language) to delimit fields of data being transmitted between the systems.
While it is ancient history now, both CP/M (and later DOS) utilized control-z (0x1a) as an end of file mark. For CP/M, the control-z flag was the only way to determine the true byte position of the "end" of a text file on a floppy disk, because the file-system did not store byte length, just disk sector length. DOS was half and half, control-z was used, but DOS also stored an exact byte length for the file external to the data within the file.
