If you’re developing WordPress sites for clients, or if you want to make the user interface a bit easier to work with for yourself or add custom content without writing code, you may well need a CMS plugin.
CMS plugins give WordPress additional Content Management System functionality and appearance. The way in which they do this varies between plugins, but they tend to give you one or more of the following:
The ability to add your own branding;
The option to remove elements form the admin screens such as dashboard widgets and metaboxes;
Improvements to the user interface, making screens easier to work with;