Design development plan(DDP) is a plan written by project manager, and it defines and describes all important aspects needed for the project. I think final scope statement is the most important part of DDP to provide understanding of project strategy, justification, deliverable, and scope of a project. I agree communication management plan is important as well for a project to be successful. The risk of insufficient planning or lack of communication may result in failure to accomplish project objectives because it contains contact information and rules for people involved in the project as described above.