I know this is going to seem like a stupid question to many of you who have been more involved with blogging, but what purpose does pinging a blog serve exactly? I have never understood that. You used to hear a lot about "blog and ping", etc. Thanks in advance.
basically you ping the RSS directories which help you syndicate your content. you can read the wiki article here for more info http://en.wikipedia.org/wiki/Ping_blog as well as my squidoo lens on RSS Feed
Though your blog will always be crawled, it is also good to ping to notify the rss aggregates on you update.
For established blogs pinging or not makes little to no difference at all. Pinging could help for brand new blogs, to get them indexed faster.