I really have no idea what effect comments have on a page. I’m just assuming that, other than showing your pages popularity to others, it also has to have some sort of effect on your keyword density for the page. That, in turn, partially effects your keyword rankings for that page.
I’m sure you’ve all had posts where people get angry with you for one thing or another. While you may not want to keep these posts, you really have to differentiate between comments that disagree and comments that flame. There are also a few things to keep in mind when editing comments.
WordPress blogs hosted at WordPress (I haven’t tried it on a self-hosted blog) make it so that you can edit comments. Not only can you edit the name, URL, and email, but you can also edit the comment itself. Now you can take out that second link people try to include in their comments, or you can edit out personal notes from friends that you don’t want others to see.
When editing a comment you should check for three things. First, the name. If you’ve seen the name around your blog before, you may just want to delete the comment. If you edit a repeat commenters comment, you might end up with a not so friendly response and lose a reader. After you’ve looked at the name, go to the URL. Change this to one of your other blogs. Free backlink for you. Third, if the email address appears fake, chances are the person doesn’t want to be known. You can edit these comments as well because chances are they won’t be back.
I have a rather good post on my best WordPress hosted blogs. It’s ranked first page for a very nice keyword. It’s regaurding the announcement of a highly anticipated product. The product has yet to be announced, and so on April 1st I put on an April fools post about the announcement. Well when they get to the end and read that it was an April fools joke they aren’t too happy. I get tons of comments. Some I leave just for laughs, but some are just to inappropriate so I edit them to include some keywords that I would like for that post.
Remember, there are comments that are okay to edit, and there are comments you should think twice about. Only edit if you are sure it won’t be checked up on for a response from you. If you have any doubt about it simply delete it to save you from any future troubles.