Ping services lets you reach or notify blog directories and search engines that your blog has a new content or has been updated. When you have a bigger ping list, your chance to get more traffic is bigger.
There are also ping services that automatically ping one or more servers each time you create a new post or update an old post in your blog. It is faster for your blog to be indexed by search engines when it is notified by ping services that you updated your blog.
Blogosphere has been growing and there are many ping services that are offering their services for free. You can also find ping services that will show you the actual ping response from the servers or whether your ping was a success or failure.
Pingoat and pingomatic are two of my favorite ping services in this list.
Here's a list ping services