Google Ranking Factor – Change Magnitude
Google doesn’t dislike stale content necessarily, but if your content hasn’t been updated for a long time and if that’s unusual behavior for a site in your genre, then you may find other sites gaining rank ahead of you.
The size and extend of changes in your website can affect how Google regards your content over time.
If you change all of your content regularly – then you might not even allow enough time for your site to be fully indexed. It takes several months – even up to a year for Google to make an accurate call on where to rank your pages, so if you change everything, you will re-set the clock in many respects.
I recommend making changes in smaller chunks if you need to update everything, and being sure to make use of technical elements like 301 redirects in case you feel changing a page URL is necessary, or when it’s a consequence of your changes.
Avoid all unnecessary changes in a URL structure because Google may temporarily see the new URL as a conflicting duplicate content to the old URL. Setting a 301 redirect will preserve most of the page-rank, but not all.
Failing to set the 301 will not only re-set the ranking clock for the page, but also potentially lose traffic to the page from link referrals and bookmarks. If you remove a page for any reason, redirect it to a valid replacement.
Some ranking factors stay in place if you do a total rebuild of your website, but many people change almost everything about their site when performing a re-design or rebuild.