If you still waste your time with Google sitemaps - it's better spent working on content or backlinks. we've done some extensive experiments on several sites running off the same (very large) MySQL database, each site with 1+ million deep pages and launched near simultaneously. we submitted full sitemaps for some and nothing for others. results across the board were virtually the same - sitemaps absolutely did not matter. in fact, in one case, submitting the sitemap was probably the reason for Googlebot to slow down crawling that site. so, in short: if your site has decent internal linking and every deep page is reachable from the root within 2-3 clicks (as it should be) - just forget sitemaps, they're useless.
well, depends upon the scenario. i found google sitemap quite beneficial for me though i don't have millions of pages but it still help full for me in crawling my pages and notifying about the internal linking issues.
I think we should not ignore the incorporation of sitemaps in our website, it should always included for the benefit of both the users and crawlers, for both  to easily navigate through your website.Â
Content building and back links are useful, no second thoughts but what I don't understand is how you can deny the importance of the sitemaps. They tell the crawlers about the other USLs on the site and they can also give you an idea of the URLs that are recognized by Search Engines in their indexing
sitemaps are only good when you're suddenly adding a lot of pages. i once used a sitemap when i inserted about 130k pages in a site in one day. i thought it would help them get indexed faster, and maybe it did. but now all those pages are indexed, and there is no need to keep a sitemap. not to mention that most of the time the google webmaster tools thing gives me a red X for "sitemap not found" or something like that, even though there is a sitemap so it's maybe good at the start if you want to add many pages, but in the long term it's useless
I do confirm Torafox statement. Once by mistake i blocked the folder where there was the site map file. There were no changes in crawling from google. On the other hand, i must say the site map has been useless to me. I moved my website from one server to another and one platform to another. I changed the directory tree of my website. 6 month afterwards i still had googlebot searching for old URLs that doesn't exist anymore. For me XML sitemap is a waste of time. I ve read Google advise people to use site map to tell what is the real URL for one page when several URL points to the same page. Nevertheless, that is not the proper way to do it. The proper way is canonical and no index metatag. Sitemap never sped up indexing or increased indexing.
I disagree. Sitemaps are not a waste of time, although they shouldn't be used in lieu of backlinks. The two should work together.
Sitemap act as a backup, in my opinion. If you site has all pages well inter-linked, then it'll be easy for each search engine to explore all pages in your site. But in most case, there are some pages not well linked inside a website, and sitemap play a good part to list all pages that you want to ranked by search engines.
I strongly disagree. Whilst sitemaps are becoming more old fashionned due to quality inter-linking, it still serves as a backbone launching point for the site as nearly every search engine still takes them into account and analyzes them for content, and they can prove useful if done properly.
Agreed , But search engine used most, people do not go to sitemap, they looking for search option for their required activity.
i think it useful , while after i submit the sitemap in google webmaster tools, it not help my site ping more frequent and i can see it do help in my SERP in minor changes. It help Google to crawl my sites correctly.
Sitemaps are not useless. One must know what is its importance and use before you can say it is useless. The fact that through sitemaps, you can determine or set the priorities of your pages over your other pages for the whole portal - and this will guide SE bots in crawling your whole website.
Sitemaps are for crawlers not for people to use. In addition, if you ad 180k pages in one day. Google will think it is spam anyways. What normal website gains 180k pages in a day? That isn't unique content. Which will do more harm then good for your site.