An XML sitemap is a document you can submit to the search engines that help guide them in determining which pages they should crawl and index on your website. Sitemaps contain a listing of all the pages on your site. And within the document you can remove certain pages you wish the search engine crawlers to ignore if they can, and which they should pay attention to first.
Some question whether or not you should even submit XML sitemaps to the search engines for the fact that the search engines may not even use them.
The truth is, they do use them. One misconception about XML sitemaps is that you should update them frequently, and each time you update a new page to your website.
I highly recommend updating your XML sitemap about once a month. In my experience, clients who try and use an automated system to update their sitemap every day, or even once a week are updating it too frequently.
The reason for this is to give the search engines a chance to actually crawl your full site and index the important content. If you’re constantly updating your sitemap, you’re constantly telling the search engines to come back only because you have added one or two new pages to your site, and doing this may actually hinder how many pages of your site the search engines are crawling since they have to come back so often.
In Google Webmaster tools, you can view stats on your websites crawl rate. To view your crawl stats simply login to GWMT, click on diagnostics, then crawl stats. Here you can view how many pages are crawled on average, kilobytes downloaded per day and time spent downloading a page.
With one of my larger SEO clients, we decreased the frequency of updating our XML sitemap from once a day to every two weeks, and after that initial two week period, we noticed a large increase in the number of pages crawled per day.
If you are updating your sitemap every day or even once a week, I would highly recommend cutting back to at least every two weeks to once a month. This recommendation may not work for all sites, but it’s definitely worth trying and see if the number of pages crawled per day increases.