Just a quick note to get some terminology cleared up:
The dash in formal English is a long mark, called the "em" dash, that is flush against the word on either side. In court reporting, back in the "carbon paper days," we had only a typewriter, and it did not have the em dash, the long mark. So we decided to use two hyphens to represent the dash.
And because we used a monofont, where everything sort of looks the same in terms of lettering, we began to use a space on either side of the two hyphens so that this "dash" would not be missed.
This "space hyphen hyphen space" is one dash in reporting. It is NOT "dashes." The question "Do I need dashes there?" is not worded correctly. It should be "Do I need a dash there?" And we use the same mark whether it is used to show an interruption or is used to mark a grammar issue.
...He was on his way to -- on the road to...
...The company initiated this program to -- this research to find out about...
...The incident was near my house -- the car crash.
...That's what I want to know -- how you intend to accomplish this.
The hyphen, of course, is a single mark that we use to tie words together into a single unit.
Be careful with your terminology. Be accurate with your terminology.
Happy punctuating!
Margie