Gary Illyes from Google posted on the Google Search blog about some of the more "hidden" advantages of using hreflang x-default value. As Gary noted on LinkedIn, "incidentally, it can also help with feeding Googlebot URLs that the poor thing otherwise might not see."
No, this is not new, as Gary said, but he thinks "it's pretty cool that it has "hidden" use cases."
Gary explained in the blog post, "While we don't talk much about it, the URLs you specify in hreflang annotations, including x-default, may be used for URL discovery. This can be helpful for large sites with complex structures for example, where it's hard to make sure every localized URL on the site is well linked."
Gary listed two additional ways the hreflang x-default value helps, outside of just helping Google Search understand your language pairs. They include this discover tip above and also a tip around conversions.
So check it out if you do any multilingual SEO or sites.
Forum discussion at LinkedIn.
