Sitemaps are one of the most important protocols for all websites as it is through sitemaps that search engines can crawl the website. It is sitemaps that inform the search engines about the URL of our sites and hence, the crawlers know about the existence of these pages and crawl them for ranking. A sitemap is an XML file that bears the list of all the URL’s on the website and a webmaster also includes additional information about each URL such as the date of last updating detail, the frequency of changes made and so on. All these details direct the crawlers and hence make the search engine work more intelligently.

The sitemaps are generally created by the webmaster on the website and the URL’s of these pages is submitted to several search engines like Google, Yahoo!, and MSN and so on. The benefits of sitemaps are as follows:

If your website has dynamic content then it is very much beneficial to have a sitemap as the crawlers can easily know the details of the content updates and can accordingly crawl it on regular basis.
Sitemaps are boon also when there are certain pages on your website that are not easy to discover for the Googlebot at the time of crawling. For e.g. pages such as AJAX.
It is lot more advantageous for a newly made website

Nevertheless, it is not necessary to generate more than one sitemap.xml file up to 50,000 URL’s. However, it is recommended by Google that you should split your sitemap.html file into more than one if the number of outgoing links exceeds than 100. But sitemap.xml file can contain up to 50,000 URL or up to 10MB file size and the webmaster can split the sitemap.xml file as per your requirements.  It is advisable to not to include those pages in sitemap which are not important for search engine (i.e.: admin pages, forms, login pages, etc) for better results.