There's a new myth going around the internet that xml files can not only get you indexed but they can also get you higher rankings on search engines, especially the number one search engine, Google.
As usual, unscrupulous companies are trying to peddle their wares to unsuspecting clients who do not fully understand how search engines work. Ferreum Corporation has written an article on search engine optimization to bring you up to speed on how a search engine works.
The idea is that if you put an xml file on your website, with descriptions and links, Google will pick up the file and give you higher rankings. This is false.
These sitemap files are really there to help you index your site with Google when changes happen or when normal navigation methods do not work.
What's interesting is that unsuspecting clients do not understand the difference between being indexed and being highly ranked. To be indexed simply means your site is in the system. It does not mean you will be found. It could be that your site is so poorly ranked due to poor copy that no one can find you. In other words, you might as well not be indexed.
To have a quality ranking, you need more than to be indexed. Sitemap xml files will not help you with better rankings. You may not even get indexed after doing all the work to get them written! Quoting from Google:
"Using this protocol does not guarantee that your web pages will be included in search indexes. (Note that using this protocol will not influence the way your pages are ranked by Google.)"
If you have been told or have been misinformed that using these xml files will produce better rankings for you, watch out. What is actually happening is that unscrupulous techniques are probably being used that will delight you in the short run and horrify you in the long run.