Use Case Diagram

From all presented diagrams, the use case diagram is the least important and beneficial. The core value of the use case lies in the use case scenario, while the diagram is just supplementary to help visualize and structure the individual use cases. The use case specification is perfectly valid, even without the diagrams.

Since the only benefit of the use case diagram is providing a visual use case overview, it is essential to state which actor performs a particular use case and to draw the system boundary. The system boundary clearly indicates which system the use cases are related to and which of them are in scope.

Without indicating the system boundary and actors, the overview is practically useless.