As the owner of a website, you have unique voice in the Internet world. On your site you publish meaningful content. It is there to be read. In order to maximize your exposure (at this moment Internetworldstats.com tells me there are about 2 billion users) you need a high ranking in search engines. This is related to a high pagerank. And the pagerank is related to the number of inbound links to your site. If it all works out, you will get traffic.
 

Now some will be willing to place a link to your site just because you asked nice. But there’s some things you can do as well. 

Of course there are quite some regularly indexed sites where you can freely place a link to your content. Take for instance Digg or Stumbleupon. But you can do more by commenting on other people’s articles and sites. In most cases you have to leave a name and email address and you can put a link to your website there as well. And that will be an inbound link when indexed. But let’s take it a little deeper.

People comment on blogs for many reasons. Most just want to express their opinion of what they’ve just read, on the topic, or maybe the other comments. Some others will comment to give positive/negative feedback or advice. And of course some people just want attention. Now if you did it for the SEO and Social Media benefits, would that be the wrong reason?
So if it's just for a quick link  you add your site's name in the box. And don't expect anything but the search engine spider picking it up. If you write a solid review and can relate to content on your site, there's more viewers. If they decide to click the link, they may want to come back for more later. It's all about the content...
 

One very good reason to comment is to tell 2 billion people how you feel on a subject, and have your voice heard. Did you ever have an opinion on a political or news post, or a scandal with a celebrity involved? It can be fun to post your comments on a blog and see the reactions. One of the great things about blogs and Social Media is that they are not a one way conversation, you can actually get involved.
 

An important use of commenting on blogs is to add to your creditability and establish your name as an expert. Are you are an expert in security and safety? Start commenting on others blogs concerning security and conflict management, evasive driving, surveillance, first aid you can let the community see your knowledge. Then have your audience come back for more if they decide to like or value your opinions.

Some will only post on their own blogs and post their own links on twitter. Commenting on other’s blogs makes you a part of bigger whole, and shows that you’re not only thinking about yourself.