[I would like to hear your comments about XML sitemap, why it is important in our Blog o Web Pages?]
Your assertion is not entirely accurate. You assert that it “is essential for the visibility of a site by search engine crawler…” which is not really true. It is helpful, but certainly not “essential”.
There are many websites, that are indexed and ranking well, that have never had an XML sitemap. Modern search engines are capable of following links from wherever they find them. A sitemap file can help them but certainly isn’t absolutely necessary as implied by the term “essential”.
An XML sitemap is a file that contains URLs without anchor text.
Perhaps you were speaking of an HTML “site map” (two words) which is not the topic of this thread. These are often confused by folks, probably because they have related functions and are pronounced the same way.