Whenever you search for a query Google shows results relating to that query ,you can also observe cached and similar pages links appearing on the results.Do you ever thought of what is this cached links about.
Google takes a snapshot of each page as it crawls and caches these pages as Backup when original page is not available , when you click cached link then Google shows page in it’s cache when it last crawled and indexed it.
When the cached page is shown you will observe from header that it’s a Google cache of blog name .it is a snapshot of page appeared when Google indexed it and current page of blog may be different.
Summary:Whenever you come across a website that temporarily down then clicking cached link will show the snapshot of that page when Google indexed last time.This will be helpful in knowing to you how the actual page of website looks .
