By default, the expression Yii::app()->user returns a CWebUser application component which represents the information that are closely related with the current user. Some information can be persistent throughout the current user session. For example, CWebUser already comes with a name property that stores the username of the current user.
Some PHP installations may use a different php.ini file for CLI PHP (command line PHP parser). As a result, when running the model or crud command in yiic shell, you may encounter errors like "YiiBase::include(PDO.php): failed to open stream..." or "...could not find driver", even though the requirement checker confirms you have PDO and the corresponding database driver.
The Yii Framework provides a sweet functionality that allows you to easily create page specific menus.
What does this mean?
This allows you to create one layout or CSS styling for your menu, and when each page is loaded, a new set of menu items is loaded in. This is useful for context specific sidebars within your application.