Depends on your site. Sitemaps can help search engines index and discover your important page URLs and content faster / more completely.
Sitemaps are important as sitemaps help search engines to index your those site pages that search engines might have missed while indexing.
Sitemap only make a sense to search engine crawler when it index pages of your website. Sitemap helps search engine crawler to reach to your important pages of website and content and in indexing your all pages include those that you have missed..
Sitemaps usually have two basic roles. HTML Sitemaps: Used to guide your website's visitors through the site, without needing to follow the url chain. Click Here for an Example. As you can see it makes the browsing experience a lot easier for visitors. XML Sitemaps: Used to guide Search Engines through the steps to "read" your website. Once you make a Google Webmaster Tools account, you can specify a sitemap in order to get a specific search view template, which looks like a tree (see the image below). So, in a nutshell, sitemaps are pretty important, in both User Browsing Ability and SEO.
Creating a quality sitemap for site is one of important on-page optimization activity. It helps Google to index your pages.
It's always nice to have place on the site where you can easily navigate and see the site structure. No matter what and how Google crawls, usability standards implies having a good organized sitemap. So try to include XML and HTML sitemaps.
According to me sitemap is principally significant if you are using javascript menus without html links or even worse stuck in the stone age with a flash website.
Sitemap helps a website to index in search engine fastly. Sitemap also help user to find all pages of a website by landing on single page.
Submitting a site map is very important to allow all search engines to index your site. Submitting these to the bing and google webmaster tools is important enough to have them ask for this information. Not having a sitemap in my option is saying that your site isn't interesting or important enough to have indexed.
A satemap is a place in your website where user can find easily any navigation key of your site. Its just like a map of your site.
If you have very large number of pages and all pages are directly not accessible through your index page, it is very wise idea to create a sitemap and submit to Google. So GoogleBot will have a better knowledge about the size and importance of your internal links and will prioritize URLs accordingly..
Sitemaps are not a new. They have always been part of best Web design practices but with the adoption of sitemaps by search engines, now they become even more important. If your site is new, or if you have a significant number of new (or recently updated pages), then using a site map can be vital to your success.