Sitemaps are still useful. Eg. my previous employer ran a very large site with hundreds of millions of possible pages to crawl. You can use the sitemaps to help the crawler prioritise given limited crawl budget.

Disclosure: work for Google nowadays but have zero insight into anything internal that's search related. The above is just common sense and should apply to most search engines.

Description tags matter in terms of converting a search to a click. So, while Google says there isn't a body for putting keywords in the description, I still do because it gives the searcher confidence that the content on the page will match their search query.

For site maps, it helps Google find updated content if you have a large site. It's not required, but it won't hurt if you submit one.

Which in my opinion, those user engaged clicks signal to Google that the link is relevant to that user for that query, especially if they stay and interact on the site. I believe that gives that site a ranking boost for that query. Those are just my opinions and cannot 100% confirm.

Also Bing seems to like sitemaps.