In your controller before you load a view, CodeIgniter will give you information regarding how fast the page loaded, how many SQL queries executed, the content of each query, and the running time of each query. This is incredibly useful when you are trying to debug your application, or simply see how quickly things are loading. There’s only one problem: To enable profiling, that line of code above must be present. What if you want to profile several pages, or even your whole web application?
He turned to another built-in feature of the framework, the controller hooks it allows, to set up a simple post-controller execution that gets a new CodeIgniter instance and enables the profiling configuration item. This is a much better option than having to put the line in each and every controller and method he might want profiled.