Completing the case for change ensures that all stakeholders understand the reasons for the change and its expected benefits. According to ACMP, this creates awareness, builds urgency, and drives sponsor alignment. Deliverables and activities (A), methodologies (C), and effort/resource estimates (D) are subsequent steps in planning but not the primary purpose of the case for change. Thus, option B is the correct answer.

(Reference: ACMP Standard, Process Group 2 -- Case for Change; Purpose: Identify rationale and benefits for change.)