Use Case diagrams are an essential tool for developers to model the behavior of a system from the perspective of its users. These diagrams depict the different actors (users or external systems) that interact with the system and the specific tasks or goals that they need to accomplish. Use Case diagrams are especially useful for developers to identify the various functionalities that a system should have, and how those functionalities are related to each other.
Want to learn more about UML class diagrams? Read everything you need to know about this way of visualizing object-oriented systems.