For developers and clients familiar with WordPress, it follows the same principles as most content management systems and enables you out-the-box to have only one content area / editor. Historically, adding additional editable content regions (for example in a two column layout) was tricky and at its most basic level was really ugly to use/update in the WordPress meta/custom fields boxes.
Elliot’s plugin is constantly updated with fixes and new features, has great documentation and has been downloaded by over 300,000 WordPress users. It is, without a doubt, one of the most useful plugins I’ve ever used and makes using WordPress for completely custom content much, much easier.
To check the plugin for yourself, visit http://advancedcustomfields.com/
Ps. Thanks Elliot!