A Sitemap (also called Site Map) is one of the basics for any website. It’s quite simple in what it does but that doesn’t diminish it’s value.
Your Zen Cart Sitemap is a list of the pages on your site. It is an XML file that lists URLs for a site along with additional metadata about each URL such as when it was last updated, how often it usually changes, and how important it is relative to other URLs on your site. All of this helps the search engines more intelligently crawl your site.
Google comment on Sitemaps is that ‘Google doesn’t guarantee that we’ll crawl or index all of your URLs. However, we use the data in your Sitemap to learn about your site’s structure, which will allow us to improve our crawler schedule and do a better job crawling your site in the future. In most cases, webmasters will benefit from Sitemap submission, and in no case will you be penalized for it.’
The Zen Cart Sitemap plugin can be configured to auto-update on a weekly or monthly schedule. This means you do not need to manually update it whenever you add, remove or update products. It will always be current.
Because Sitemaps are supported by all the major search engines, you only need the one version for everyone. A nice convenience in these days or proprietary this and that.