form my point of view I think sitemaps are useless and my have adverse effect and may harm indexed urls why? 1- read this carefully from Google :'You can add a Sitemap to your account to provide us with additional information about your site' 2- some sitemaps when added google does not crawl other pages, so you must put all site links in the map which is difficult 3- think how google view web sites : is it possible to make a site that have a site map appear over a site without a sitemap just for this? no for sure so i think sitemaps is for indexing a site with links google could not crawl, which is rare , however submitting a sitemap may decrease your indexed URLs what do u think?
Sitemaps can't be the cause for having less web pages indexed in Google. It can only help bots finding content which has has low link juice either internally or externally.
sitemap are helpful. What you think you have research too much to give the fight to the developers of sitemaps.
Sitemaps are now a necessary for professional web sites. They tell Google (SEs) when a page has changed, or that a new page has been added. We do not create these by hand (programming), we us gSitecrawler to create it. It is free and works with very large sites.