The Controller::set( ) method is just a way to pass a variable from the controller to the view. The basic syntax is $this->set('varname', $value).
There isn't really a formalized or "right" way to use the method, or how to name your variables. Just code to preference.
However, $this->data and $this->params['data'] (functionally equivalent; the former was added post-1.0 for the sake of less typing) are special variables that get passed to the view automatically. They have special significance for form fields and the like.f2富二代官网入口