I have a client that has a HUGE website with thousands of product pages. We don't currently have a sitemap.xml because it would take so much power to map the sitemap. I have thought about creating a sitemap for the key pages on the website - but didn't want to hurt the SEO on the thousands of product pages. If you have a sitemap.xml that only has some of the pages on your site - will it negatively impact the other pages, that Google has indexed - but are not listed on the sitemap.xml.