Let's look at the action
edit in a controller.
def edit end
In the above method, it is not clear whether that method's implementation is complete or not, since developers sometimes forget to complete the method.
Here is a way to remove that ambiguity.
If the implementation is complete,
then just add the word
def edit render end
Now, when one looks at the method, it's clear that the developer did not forget anything. The developer is explicitly saying that the only thing this method does is render the view.