I was looking through the Oxford Dictionary and came across an admonition on the sue of dashes ( -- ) .  The Dictionary sys that a dash should never be used in the placee of a comma.

That's likely true for formal prose, but it's bad advice for the digital writer.

A dash is unmistakeable in setting off a list or subordinate clause for readers, especially those trained to read from a screen.   Little marks (bumping up to the last letter of the preceding word) can be easy to miss.  A dash set off by spaces between letters helps the reader make a more efficient connection between the main idea and the subordinated ones.