If you are working on a big project then it is important to keep your CSS maintainable. Quoting the article: "CSS with this much repetition is also expensive:

If you are working on a big project then it is important to keep your CSS maintainable. Quoting the article: "CSS with this much repetition is also expensive: It’s expensive to create, and it’s particularly expensive to maintain (not even variables will save those who, on average, repeat each declaration nine times, like the Engadget and TED teams)."