$this->render ('topnav.phtml')
$this->partial('topnav.phtml')
Render has the same variable scope as the script from which it is being called. Therefore, we must be careful of variable clashes. while partial helper render a view script within its own scope. There is one downside to partial helper though, it has to clone a lot of objects to get the view into its own scope, which means there is a performance hit while using it.