I took an informal poll on Twitter, and here are the (blurry) results:
Honestly, I was a little surprised—but not too surprised. Writers in all forms have commonly, maybe even traditionally, used italics to emphasize a word or phrase in the text. But I guess I thought more people would recognize boldface not merely as an alternative but as the preferable alternative.
Personally, I prefer bold for emphasis in brief writing because italics are already used for so many other purposes. Case names, foreign-language terms, and the titles of books and journals, for example, are italicized. So why inject more italics into your brief by also using them for emphasis?
We typically use boldface only for our headings—but that’s actually because we’re trying to emphasize our headings (i.e., to create some contrast between our headings and the main body of our text). Thus, whether we realize it or not, we’re already using bold for emphasis. So why not use it consistently for emphasis wherever emphasis is needed? Makes sense to me.
Also, an upside to using bold for emphasis is that it really stands out on the page. I know, I know. Duh. That’s what “emphasis” means, right? No, that’s not what I mean.
What I mean is this: we should avoid using typeface to create emphasis. We should craft our sentences so that emphasis is created naturally—by rhythm and grammar and syntax—instead of relying on an artificial change in the typeface. Changes in typeface are distracting to the reader. Good writing can create emphasis without having to resort to these distractions. Sometimes we might still want to use typeface for emphasis. But, whether we’re using italics or boldface to create this emphasis, we should inject these distractions as seldom as possible.
And, as I was saying, an upside to using boldface is that it really stands out on the page—so you’ll be more reluctant to use it. The problem with italics (as noted) is that we already use them all the time, so they don’t leap out at us as much—which means, in my opinion, we’re more likely to overuse them.