Why design custom 404 pages
A rising online trend is that of the custom 404 page. Many of you have likely have heard of or have seen Twitter's "fail whale" which is a great example of a well-designed error page. Custom error pages are often quirky, fun, or even tongue in cheek. These pages often poke fun at the website for making such a silly mistake.
By default, Apache (the most prominent web server software), serves up the same old bland, text only pages that you normally find when you click a broken link. Customizing these pages can be helpful for a number of reasons:
1. Error pages will be displayed in line with the established style or look and feel of your website / brand. This makes them feel much less like error pages and more like pages that are meant to exist on the website.
2. Placing expanded navigation or even a search input on an error page could help allow the user to find their way to the content they are trying to locate.
3. Promotional content or even advertisements could be displayed on this page in order to take advantage of the page view or to expose the user to new sections of the site