The term SiteMap means a few different things in different contexts. There is a page at siteroot/SiteMap.aspx that is a site map for visitors of your site to see the entire site hierarchy, its linked from the Site Map link in the skin.

google does crawl the site but it doesn't do anything special about the site map page.

There are 2 other site map urls in mojoportal that are specifically for google, but google doesn't know about them automatically, you have to submit them to google webmaster tools. siteroot/SiteMap.ashx is the main site map to submit to google for your site, and siteroot/BlogSiteMap.ashx is a site map you can submit to google to help it crawl your blog posts.

Submitting these site maps to google helps google understand your site better when crawling it and can improve your SEO (Search Engine Optimization)

So, in short, mojoportal generates these 2 site maps for you that are specifically for submitting to google webmaster tools.

Note also that the site maps for google indicates how important each page is within your site and also indicates how frequently the page is updated as well as the last update time. You can adjust the priority ranking and the expected update frequency for each page in the main menu by going to Page Settings for any given page and go to the Search Engine Optimization tab. Priority ranges from 0 to 1 with 1 being the highest priority.

Hope it helps,

Joe