Using sitemaps has many benefits, not only easier navigation and better visibility by search engines. Sitemaps offer the opportunity to inform search engines immediately about any changes on your site. Of course, you cannot expect that search engines will rush right away to index your changed pages but certainly the changes will be indexed faster, compared to when you don't have a sitemap.
According to me sitemaps are a significant technique of communication with search engines. While in robots.txt you tell search engines which parts of your site to exclude from indexing, in your site map you tell search engines where you'd like them to go. Using sitemaps has lots of benefits, not only easier navigation and enhanced visibility by search engines. Sitemaps offer the chance to inform search engines instantly about any changes on your site
Sitemap - How important it is?