Google bot really crawl based on sitemaps?

I'm confused that someone say Google sitemaps is only useful for fun, the
bot crawl the site as per its own way.

 

XML sitemaps are a create way to show search engine crawlers all the available URLs for your website, yes in theory a web spider can find all your pages on it's own, but why not lend it a hand.

 

Thanks ssandecki

 

If you dont submit .xml in google although google will index your pages. If google index your index page then it follow your internal linking structure and based on that index all other pages. But with .xml you can suggest google to crawl those pages frequently.