Google's John Mueller said on Twitter this morning that Google doesn't really care much about the priority field in the XML Sitemap, but they do care about the URL and last modification date. Here is the tweet:
The URL + last modification date is what we care about for websearch.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) August 17, 2017
We know Google doesn't care about the priority field, Google has said that time and time again.
But Gary Illyes back in 2015 said Google ignores last mod date in Sitemaps for the most part. Here, John seems to be implying the opposite.
It might be that Google actually has their own last modification date based on looking at the page on date X and then on date Y and noticing a modification. Maybe that is what John is talking about. Or maybe Google now does look at the last modification date in the sitemaps file?
I am waiting for clarification from Google on this...
Forum discussion at Twitter.
Update: Here are more details from John on this:
It's no secret: we want to know when something new is on the website so that we can crawl it. It's not magic, we just can't read minds. Yet.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) August 17, 2017
If you spend more time updating the lastmod field than improving the website, you're going to have a bad time. Focus on important things.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) August 17, 2017
