New to Java

On this forum some time ago, I think I remember the comment: "Do not subclass unless you change the behavior of the parent class".

That makes sense to me. Yet, in many tutorials I see classes that subclass JFrame and do not change the JFrame behavior. More generally, subclassing while not changing behavior is poor OOP and not the proper use of inheritance, right? This is valid criticism? The JFrame subclassing seems only to be done for convenience?