Plugins SDK is useful to develop layout templates and make them hot-deployable. In short, you can update, deploy, and test layout templates in Plugins SDK without restarting your application server. Plugins SDK is also helpful to develop themes. It manages the differences between existing themes, creates a plugin WAR file with the resulting theme, and it is able to install the theme in a local installation. More importantly, everything in themes is customizable.
Moreover, Plugins SDK is helpful in developing portlets with a hooking feature. Portlets developed in Plugins SDK only import classes from
portal-kernel.jar, portal-service.jar, and other JARs contained in the portlet folder