If you put the same priority levels for your URL included in the website XML sitemap; then Google Webmaster Tool can possibly give you a red marked WARNINGS which indicates the following lines -
All the URLs in your Sitemap have the same priority.
All the URLs in your Sitemap are set to the same priority (not the default priority). Priority indicates the importance of a particular URL relative to other URLs on your site, and doesn't impact your site's performance in search results. If all URLs have the same priority, Google can't tell which are more important.
Now, this is the time when we also need to check the priority of the website URLs. Either we have to manage low and high priorities to the web pages included in the XML sitemap or have to set a default priority.