A lot of my pages disappeared from Google's ranking as soon as I started using this software. It may be a coincidence. These pages are static pages but do not show up in the site map because they are date/expired "products", but until very recently they still ranked. I am GUESSING Google will use the sitemap as a reference for content to index/show in their results. If it isn't in the sitemap, it loses clout. In my case for the most part this is not a big deal but if the page suddenly becomes active on my site again there will be a delay before ranking again which really isn't good for what my site does.
Like I said that is a guess and it may be coincidence.