Google Sitemaps have a Refresh Frequency parameter (Change Frequency) that tells GoogleBot how often a web page is updated. For example, a blog homepage can be updated as often as "daily", while the individual blog entry entries are updated "never". The correct setting of the update frequency of the links in a Google sitemap is of crucial importance for search engine optimization (SEO).
Make sure that you keep your update frequency for individual posts (which do not change significantly) at "Never" or at most "Year". Based on our experience, I recommend setting this to "NEVER" for large websites (blogs, forums) with hundreds of thousands of posts (pages) that change rarely or never.