Good question - there is generally slight confusion between Scope and requirements and hence scope management plan and requirements management plan.
A requirement is a condition or capability that is required to be present in a product, service or result to satisfy a contract or other formally imposed specification; where total scope is the summation of products, services and results to be provided as a project.
Product Scope: The features and functions that characterise a product, service or result.
Project Scope: The work performed to deliver a product, service or result with the specified features and functions.
Scope is mainly about tasks or actions required to complete the product or project whereas requirements, on the other hand, are features, or specifications you intend to build as a result of the project. Requirements are ideas you want to implement.
SCOPE MANAGEMENT PLAN is written with following in mind.
• How will the Acceptance criteria be derived
• Who all needs to be involved to prepare a complete and foolproof Work Breakdown Structure
• How do we handle changes to WBS. Who will review and approve ? Overall how do we handle changes in the project scope. ?
• How do we prepare a good project scope statement?
REQUIREMENTS MANAGEMENT PLAN
• Requirements traceability and tracking the implementation w.r.t plan
• How do we handle changes, missed requirements, additional requirements ?
• Prioritising the requirements - Nice to have vs Must have
• How do we measure and check if the project is really on right track and meeting the requirements.
These documents are mainly for planning and do not deal with actual scope or requirements of the project. A good planning is very essential step and it will help minimize conflicts and misunderstandings. These documents will serve as guideline on what needs to be done when there are issues with scope/requirements. A good planning serves as foundation.