If you want to take advantage of Google Sitemaps, you need to place a Sitemap-formatted file on your webserver. By doing so you enable Google's crawlers to find out what pages are present and which have recently changed, and to crawl your site accordingly. Google Sitemaps can help to get more of your web pages crawled and can also enable you to tell Google when contents on your site changes.
This sounds pretty good. However, the problem I see is that in order to get started, you have to install some scripts on your sever. Webmasters "should have knowledge of uploading files to their webserver, connecting to their webserver, and running scripts. In addition, Python version 2.2 must be installed on your webserver - check with your web hosting company if you are unsure". Bottom line: you have to be a technical guy or have a technical guy to help you in order to take advantage of Google Sitemaps. To make people's life easier, Google also says "If any of these requirements are not met, you can still submit a Sitemap to the Google Sitemaps program in simple text format.".
Here is Google Sitemaps' FAQ.
Website owners should take advantage of Google Sitemaps to get better seach engine visability.