Which best describes the role of non-functional requirements in system design?

Non-functional requirements are critical in system design as they define the overall quality attributes of the system, such as performance, usability, reliability, and security. These criteria help stakeholders understand how the system will perform under various conditions and ensure that it meets the user's needs beyond just functional capabilities.

For example, a non-functional requirement might specify that a website needs to load within three seconds to ensure a good user experience, or that the system should handle a certain number of transactions per second to remain efficient. By outlining these performance metrics and usability criteria, non-functional requirements help guide design decisions, enabling developers to create a system that not only operates correctly according to functional specifications but also meets or exceeds user expectations in terms of quality.

In contrast to the correct answer, other choices depict limitations or misconceptions about non-functional requirements. They are not merely supplementary documentation; they are essential components of the system that influence how it will be built and interacted with. Moreover, they should not be omitted during any documentation phase, including when outlining use cases, as they play a crucial role in ensuring that the intended experience and requirements are fully communicated and addressed.