The purpose of ping scripts or services is to rapidly have search engines detect a new website or blog. Often times, Google is pretty good at detecting new websites, especially if you run a search query for your domain name. You can also add your website to Google Webmaster Tools and go to Crawl > Fetch as Google.
The benefit of mass pinging is to stimulate the discovery process, especially for all of the additional smaller search engines. If you’re lucky, you might also get some temporary back links from crawler sites such as Alexa.com, depending on the list the ping script or service uses.
Here are two free services for general SEOs:
If you’re an advance SEO and are familiar with Scrapebox, you can download my mass ping sites list, which is very comprehensive and has 50,000+ URLs. Please note I am against using Scrapebox to generate blog commenting backlinks, as those are spammy and can lead to getting de-indexed on Google.