As a developer I use this on every WordPress install for client sites.
It exponentially enhances WordPress as a clean, clear and viable CMS for clients to use. Simply choose which fields do and don't appear on each page, template or post-type.
Combined with custom post types and hiding any unnecessary menu items I don't even have to send a CMS guide or teach clients how to use the admin area anymore anymore. Simply fantastic!
The additional plugin add-ons (notably the gallery and repeater fields) are a bargain too for the functionality they add and that they are multi-use dev licences.