Sometimes we need some complicated view to be displayed (such as generating complicated table). Most people suggest that in MVC the View must be as simple as possible (don't have too much loops, etc). So what we have to do is to hide away the complex code by putting it at somewhere else. The following are few places options to keep the function:
One of the common requests I see in the forum is how to implement RBAC. While you can implement Yii 2's built-in RBAC, that might be too much for developers who are just starting with Yii 2 or have simpler needs. Sometimes you are looking for a fast solution and just want two flavors, user and admin. And even if you will eventually need more, you can use these methods as a starting point for developing your own features or move on to Yii 2's RBAC.
I assume you are familiar with accessControl standard filter. It allows you to separate privileges to run some action from action code itself. There is however one problem with most common usage - you cannot use bizRules, at least based on some parameters passed to 'checkAccess' just because it is hard to pass them in accessRules() result.