anallawalla - 2:51 am on Jul 20, 2012 (gmt 0)
Like Tedster said, A sitemap.xml begins to help a site with a large page count -- in the millions. I once managed a site with 74 million URLs. It was never fully crawled and indexed, but the priority hint values helped to ensure that the higher level (e.g. category, city etc) pages were picked up first.