Like many webmasters, when Google Sitemaps was released on 2 June 2005, I immediately created 
and submitted XML sitemaps for all my websites, keeping my fingers crossed that Googlebot wouldn’t find any errors when he finally downloaded them. At the time, Shiva Shivakumar posted to the Official Google Blog:
We’re undertaking an experiment called Google Sitemaps that will either fail miserably, or succeed beyond our wildest dreams, in making the web better for webmasters and users alike. It’s a beta “ecosystem” that may help webmasters with two current challenges: keeping Google informed about all of your new web pages or updates, and increasing the coverage of your web pages in the Google index.
Webmasters expected big things from this experiment. Site owners hoped this would finally mean perfectly crawled, complete indexes of their websites that were regularly updated and would increase their rankings. Most were disappointed and decided to abandon Google Sitemaps almost immediately. Google Sitemaps: A Useful SEO Tool?