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AnkitMaheshwari - 10:43 am on Jun 30, 2011 (gmt 0)
One of the use of XML sitemap of a very large site is that the sitemap section of webmaster tool gives number of URL's indexed in Google and any anomaly (say penalty to a section) might get detected early if you are looking at this number periodically.
I regularly keep track of it as site: operator give too vague numbers(at times)....