A sitemap document lists all the pages of a website one would like to submit to search engines. Once submitted to Google for example, their robot crawlers would visit your website at a regular basis in order to index the content effectively. For Prestashop content includes product pages, category pages. I can also add images, blog posts, videos and so one. Clearly Sitemap helps search engine learn about your website. It quite important to accelerate the way search engines index your content.