The task Trace Requirements ensures that requirements and designs across different levels (business, stakeholder, solution) are consistently aligned with one another. This alignment supports scope management, impact analysis, verification and validation efforts, and change control.
Requirement tracing also:
Clarifies relationships between business needs and solution features.
Enables efficient scope monitoring and helps avoid scope creep.
Supports linking requirements to their source and derived components.
BABOK Guide v3 - Section 5.1: Trace Requirements:
"The purpose of Trace Requirements is to ensure that requirements and designs at different levels are aligned to one another and to support change analysis, coverage, and allocation."