Most reporters use the dash simply for that ever-present interruption. There are, however, grammar rules associated with the dash.
Here's one:
When an indefinite pronoun follows ONE word and renames it, there is most often a comma.
When an indefinite pronoun follows MORE THAN ONE word and renames each word, there should be a dash.
...He took medications, some of which helped.
...He took medications, supplements, and vitamins -- some of which helped.
...I brought cupcakes, all of which were a hit.
...I brought doughnuts, cupcakes, and banana bread -- all of which were a hit.
...She brought her friends, each of whom contributed something.
...She brought her family and friends -- each of whom contributed something.
Happy punctuating!
Margie