What is the purpose of non-functional requirements in a requirements specification?

Non-functional requirements play a crucial role in the requirements specification as they impose constraints on various aspects of the system's design and implementation. These requirements define how a system performs certain functions rather than detailing what specific functions it must accomplish. Non-functional requirements often relate to attributes such as performance, security, scalability, and usability, which guide developers in making design choices that meet the overall goals of the project.

By clearly outlining these constraints, non-functional requirements ensure that the system not only meets the functional goals but does so in a way that aligns with user expectations and operational demands. For instance, specifying that a web application should handle a certain number of concurrent users or respond within a particular time frame directly influences design decisions regarding architecture and resource allocation. This focus on quality attributes can significantly impact the system's overall success in real-world usage.