We have a sitemap.xml file at work, I made it to check a box in some tool a consultant ran for us. I think it was a giant waste of time, but making it was easier than arguing.
Categorically I think sitemap.xml is useless iff:
- You generate it using any sort of online tool
- You don't spend a lot of time customizing the output of the generator.
Why? Because the way those tools work is to crawl your site and find pages. You know who is really good at crawling sites to find pages? Google/Bing/Baidu. Probably way better than the online tool you found, plus those search engine crawlers have also crawled millions of other sites and found parts of your site already.
Using an online generator, and uploading the file is like like finding an airline pilot and letting them know that it's pretty helpful to have wings when you fly. They know that already, and they also already understand the nuance of the situtation a thousand times better than you. You've just wasted their time, if they're polite they'll smile and nod and move on. Just like Google.
Rather than wasting time building a sitemap that google doesn't need, put those 5 minutes into fixing literally any other SEO problem on your site. Screw it, just write a low effort blog post. You'll get better results.
Is sitemap.xml always a waste?
If you actually put effort into customizing your sitemap, pointing search engines at pages you want people to find, and devaluing pages you don't, use a sitemap. Or use another tool like meta-headers.
Further Reading: Moz has a great article on XML Sitemaps.