As far as I know, there are only two reasons why you need to post comment on blog.

First is to market your business. Blog commenting is one way for to attract visitors to your site. Since the blog owner regularly is checking the blog, the owner will surely read you comment and possibly click the link you posted there. In this case, the blog commentor has gained a unique visitor of the site and a possible client in the future.

The more blog where you posted a comment means the more possible client you may get in the future. For this reason, web masters and programmers have developed an semi and auto blog poster machine to ease up this another monotonous task. It is monotonous in the sense because you have to go on and on to the blog’s single post where the comment box is located. Not all of the blog commentor, but many of them are thinking this way – to market their own products or services

The second one. You need to post a comment on blog because you are developing a link popularity to the search engines especially Yahoo where comments are considered links and could appear in the search results depending on the number of links a website may have.

Most bloggers particularly those who are already in the blogging industry are already blind about these comments. As mentioned above, blogs are regularly updated, so the owner knew already when a comment is a blog spam comment or not. For the reason, the owner is no longer reading such comment, instead, just click on the spam comment option and click the moderate comment button with even considering other comments.

Since you want to have your link to be live in that blog via the comment box, isn’t it better to think first what to be posted as comment before clicking the submit button? Obviously spam comments are posted with out even reading a single sentence in the post. This is why there are lots of blog comment where comments are in any way doesn’t have any connection the post being commented.

So, to make your comment to be approved by the blog owner, you should at least read some part of the post. In this way, you could think of a more appropriate comment to post on. If your comment is approved, you did not only created another backlink for your website, but also gained another unique visitor and a potential client of your business.