Why need 404 page
 

Search engine spiders in request a URL for "404" state response, namely know this URL has failure, then no longer index this page, and to the data center feedback will the URL of the page said from the index database to delete, of course, delete process there may be a need for a long time. And when the search engines to get "200" state code, will think this URL is effective, they will go to the index, and will include it to the index database. So, custom error page 404 not only enhance the user experience of good practice, but also to the search engine is also very important.