In my BPMN Method and Style training, I show the following BPMN and ask students, "What does this diagram say?" You really cannot tell. It says something happens and then either the process ends or something else happens. Not very informative. But if you run Validation against the rules of the BPMN spec... no errors! As far as the spec is concerned, it's perfect. But if the goal is to communicate the process logic, it's useless.