When enhancing an existing product, which documentation is least useful?

When enhancing an existing product, the full history of retrospective plans and lessons learned is least useful compared to the other options. While retrospective plans and lessons can provide valuable insights into past issues and team dynamics, they do not directly inform or drive the enhancement of the product itself.

The current codebase is essential as it represents the existing functionality and architecture of the product. Understanding how the code is structured helps developers implement enhancements and ensure compatibility with existing features.

User stories are vital as they empirically express user needs and feature requirements, guiding developers on what enhancements are necessary and how they align with user expectations.

The product roadmap outlines the vision and future direction of the product, including planned features and improvements. This strategic view is crucial for prioritizing work and ensuring that enhancements fit within the overall plan for the product landscape.

In contrast, while retrospective plans and lessons learned offer retrospective insights that can inform team processes and interactions, they provide less immediate value in terms of direct product enhancements. The focus in product development is typically on current requirements and technical foundations, making the retrospective history less critical in this context.