[ozzy47]

What’s the use?
On a 404 page usually you want to let people know something went wrong and the page they wanted to see is not available.
But after you let him know what just happened, an advantage the 404 page offers is that you are able to suggest other pages he might want to see or give him instructions to get to an active page. Using a customized 404 page, visitors won’t get confused and leave the website not knowing what happened. If you decide not to have a customized 404 page you should know that a non-customized 404 page can look not so friendly.

Customized 404 Pages and Search Engines
Search engines also can benefit from a 404 page. Imagine that a link is broken and it leads to a non-existent page. At this point search engines can’t go any further and won’t index content. If you choose to have a customized 404 page even though a page is broken search engines will see a page that can be indexed and can find links to pages that could benefit from a crawling. This is an SEO benefit!

404 Pages bring credibility
Having a non-customized 404 page looks unfriendly. But imagine a scenario where a visitor ends up on the 404 page and is shown a nice image, some instructions and links to other pages he might be interested in. He will thing that you really care about his experience on your website and probably he will go to a page you suggested and won’t leave your website or hit the back button