Nearly all new bloggers think that blog commenting can improve their website's PR (Page Rank) and traffic. So they blindly keep commenting on all posts they read and find a space to fill website link in comment section. It is true that back links from a high PR web page also improves the PR for linked pages. But does blog commenting really improves PR and traffic?
About Traffic Explode
Many people like to know views of different people on the topic, so they read comments left on the page. And they got more curious about the commentator when they found something interesting. Here you can win for head and tail both. They will follow you if their opinion and your comment matches. Wohoo!!
In the other case, then also they will follow you if your comment is just opposite to what they think. So, in either way, you are getting traffic. But do not post comments just for getting traffic. It should be natural, meaningful and off course relevant to the topic. If possible, use only your real names and not your blog's title for comments.
About PR (Page Rank) Policy
No doubt that back links improve PR and off-page SEO for your blog. But the relation matters. The relation defined by 'rel' tag that you see within the <a> tells web crawlers to vote for the link or not. And blogs take advantage of this. They define rel="nofollow" to all external links generated by visitors to tell search engines that they are NOT voting for the link that follows. All major search engines including Google, Bing and Yahoo respect this tag for ranking calculation.
Though you will hardly fine one, you can always view the source code of any website to check whether it is using nofollow or dofollow or something else. It will add value for anything other than a nofollow.
Conclusion
Blog commenting doesn't lift your PR at all, but it can give you traffic. Rest depends on your content to attract this traffic as regular visitors and start following you.