You need traffic on your site. After all, without traffic you might as well not have a website or blog. One of the ways that people are trying to get that traffic is through commenting on other blogs. Just like everything else however there are ways to make that strategy work for you and ways that make the whole thing pointless.
For instance, being the first response on a blog may seem like a good idea, but the reality is that your focus on commenting first can make you sound like a spammer rather than encourage clicks through to your site. Brian Clark recommends picking blogs that you actually like, and then use the comment area to build a relationship with the writer. Writing relevant remarks will encourage people to take you seriously and take an interest in your business.