If your WordPress (WP) site is going to support comments, then Akismet is a requirement. Letting comments appear on your site without any moderation is an open invitation to porn site and other SPAM comments. WordPress supports comment moderation ranging from the requirement of having an administrator approve every comment before it is displayed, to all comments appearing as soon as they are entered.
Moderating every comment is a lot of work. If you expect few comments on your site, approving every one is the safest approach. If you want a lot of comments, then remove all approvals and turn on Akismet. Akismet is a plugin that scans each comment as it comes in and moves ones it suspects as SPAM into a SPAM area that requires approval. All others appear immediately.
There are two possible problems areas of this approach: missing a SPAM comment or suspecting a valid comment is SPAM. My experience with Akismet has been positive. I find it occasionally puts a valid comment in the SPAM bucket, but seldom misses SPAM.
Best of all is the installation. Nothing could be easier, as Akismet is included with WordPress. All you do is go to Plugins and activate Akismet. For Akismet to work, you will need an API key. Go to http://wordpress.com/signup/ and sign up for a WordPress.com account. Your API key will be emailed to you as part of the confirmation message. If you already have a WordPress.com account, your API key is listed on your profile page, which you can get to by clicking the “My Account” link in the top right when you’re logged in.
Once Akismet is activated, you will see three types of comments in the Comments administration area: Pending, Approved and Spam. If you have multiple WordPress sites, you need only one API key for all of them.
By using Akismet, comments appear automatically on my sites, but SPAM comments await moderation.