Overview:
This artifact captures the sequence of actions a system performs that yields an observable result of value to those interacting with the system.

Purpose:

The primary purpose of the Use Case is to capture the required system behavior from the perspective of the end user, to achieve one or more goals. Different users benefit in different ways, of course:

• Customers use them to describe, or at least to approve, the description of the system's behavior.
• Potential users use them to understand the system's behavior.
• Architects use them to identify architecturally significant functionality.
• Developers use them to understand the required system behavior so they can identify classes from the Use Cases' flow of events.
• Testers use them as a basis for identifying a subset of the required Test Cases.
• Managers use them to plan and assess the work for each iteration.
• Technical writers use them to understand the sequence of system behavior that they need to describe in the documentation.