An XML sitemap is a file, usually at /sitemap.xml, listing the URLs on a site along with optional metadata like lastmod (when a page last changed). Submitting one — via Search Console or a Sitemap: line in robots.txt — doesn't make Google index those pages, and it doesn't improve their ranking. What it does is give a crawler a direct list of URLs to check, which matters most for pages that are hard to discover through links alone: a new site with few inbound links yet, a large catalog where some products sit deep in the navigation, or a page that changed today and you'd like recrawled sooner rather than whenever a crawler stumbles onto it again.
What belongs in a sitemap
Only URLs you actually want indexed: canonical (not duplicate) URLs, returning 200, not blocked by robots.txt, and not marked noindex. A sitemap entry is a claim — "this is a real, indexable page" — and every entry that doesn't hold up erodes how much a search engine trusts the rest of the file.
Sitemap index files for large sites
A single sitemap file is capped at 50,000 URLs (and 50 MB uncompressed) by the sitemap protocol. Sites past that size use a sitemap index file — a small XML file listing multiple child sitemaps, each under the cap — so a million-URL site might ship one index file pointing at twenty 50k-URL sitemaps split by section or crawl date. Search engines fetch the index first, then work through each child file at their own pace.
noindex'd pages, robots-blocked URLs, redirects, 404s, duplicate/parameter variantsThe mistake that undermines trust in the whole file
The single most common problem in sitemaps we see on real sites: URLs that are noindex'd or blocked by robots.txt still listed in the sitemap, usually because the sitemap generator and the page templates drifted out of sync after a later change. Submitting a sitemap full of URLs a crawler isn't even allowed to fetch is a contradictory signal, and repeated contradictions make engines trust the rest of the file less, not just the bad entries.
Because a sitemap has to track the site's actual indexable state, not a one-time export, RacingRoach can generate a valid, size-split XML sitemap straight from a live crawl — so the file reflects what's really crawlable today, index-split automatically past 50k URLs, instead of a document someone hand-maintained and forgot to update.