In a sitemap, is it important to include information about when the url was last changed in a <lastmod> tag?
How does not including a <lastmod> tag in a sitemap affect how my site is crawled?
If I leave this information out, how does it affect indexing in search engines?
According to the protocol definition this is an optional tag.
Most crawlers tend to ignore the lastmod tag as many webmasters do a poor job of keeping it up-to-date and forget to update it when they update content on the site. A sitemap is still important to identify content on the site but even if the lastmod tag shows the content hasn't been updated since the last crawl the crawler will still crawl it to confirm the content hasn't changed.
