Most applications will have one or two sidebars and often you want to control the content that should appear in the sidebar based on the action. For example you will want to show something different on the homepage as opposed to some view page. While achieving this you generally also want to avoid putting the layout into each view, as that would mean if you wanted to change the layout (e.g. put the sidebar on the left instead of the right or do some funky layout which requires an additional div tag to be added) you'd have to go through every view, which does not achieve good code re-use. It is also bad practice to have lots of if statements in column2 layout just so that you can generate the sidebar correctly.
I (www.jamesbarnsley.com) found that when using the Yii Bootstrap tabs component you will sometimes want to direct the user to a specific tab and not necessarily the first tab. Yii Bootstrap already provides the "active" variable so you can define whether the tab is the active tab or not in PHP. I generally find though that a PHP solution to this problem is rather cumbersome as every tab component will need the PHP code inserted or you will have to extend the tab component somehow to do it.