To understand how pinging your site be beneficial, you have to understand what “pinging your site” is all about. To ping your site is sending the link or even feed link of your website out through one or many services that help index your site faster. It also tells search engines your site is updated.
Some of these places may be article sites where they give you a back link to your website and post the title, link to the original page or article, and a short description. Some of the sites out there may send your article to those places for you quickly (somewhat like social bookmarking.)
With search engines that you update your site with, your site will be ranked amongst others that have similar descriptions, titles, keywords, and more. For those who optimize their pages already, and even ping their site, it could mean a better listing.
It can be tedious to enter in your links to ping sites. Some of the ping sites out there are free to use. Some are free, but have limitations, and others for mass submission have a fee. It is at your own risk if you want to pay to use any of the services out there, so do a little research to make sure they are reputable.
Side note: Also, there are people on Fiverr (as of July 2011) that will submit for you too. However, from my own experience, many of the places submitted to were 404 errors, so please keep this in mind and only use at your own risk.
Often, I hear bloggers ask why they should spend so much time to ping sites if the back links do not have much quality. My answer- while you may not have the time, you can certainly schedule to ping your site sometimes… perhaps once a week, or twice a month. I might not recommend pinging your site constantly. Some sites do have rules and it could get your banned from using their services.
Now, for users of WordPress and some other CMS, you may have a built in pinging service that you can put the links to the places you want to notify of your updates and submit your updates for you.
Do you ping your site? How often do you? What ping services do you like to use?