What are the documents that are considered input to a project resource and project communication plan? Where are each knowledge area used within the 5 process groups for a project? What are the key reasons a project requires a plan for each of these?

Management DQ2

What are the documents that are considered input to a project resource and project communication plan? Where are each knowledge area used within the 5 process groups for a project? What are the key reasons a project requires a plan for each of these?