A lot of writers use dashes and parentheses interchangeably or use one or the other exclusively. Both approaches are wrong.
As I’ve mentioned earlier, em dashes highlight big ideas. Parentheses, however, are used to contain details. If the information isn’t essential to the sentence, put it in parentheses. If it’s vital, use dashes. Here’s an example:
A former American Idol contestant—Antonella Barbra—is the most-searched for person on the Internet (and I am shamelessly including her name in this post to drive traffic to my site).
Put another way, if it’s information you want to downplay, use parentheses; if it’s something you want to resonate with your readers, use dashes.