In large projects where project monitoring is necessary a PQP that supports your  PMP is an excellent reference document. The PQP creates workable boundaries, identifies key issues of quality and creates a preventative plan and a document to work from that is clear to all.

Again this is to give greater clarity to the Project Management team of what is expected in the Project disciplines and also give guidance on how to monitor the project against the Project Management Plan.

The PQP needs to be edited and approved by project management before the relating project is commenced. Issue management needs to be clearly stated in the Project Management Plan and it should also give guidance on how issues are to be resolved with external parties.

Having this support documentation agreed before the Project Start, allows the project to be audited in an open manner with no surprises to the Project Management team.