From the original article: "Did you know that major search engines want you to make video sitemaps for all of your embeds, even if you're hosting on Vimeo or Youtube?
Not only does it help them spider your website by giving the search engines clues as to where to look for video embeds, it may also earn your site a click through boost by giving you a picture in the SERP.
There are several reasons why you'll want to add a video sitemap.
It makes it clear to Google what your content is.
You have the opportunity to provide a range of details through schema.
Additional presence on video.google.com search.
RAD picture thumbnail, which is a pretty great call to action."
Via Robin Good