A project purpose manager is any user with a role that contains the privilege PRIVILEGE_MANAGE_PROJECT_PURPOSES. By default, the privilege is contained in two roles: build_mgr and ccm_admin. Each site can add or remove this privilege from any role.
A project purpose manager can create or delete the project purposes for a database. However, if a build manager tries to modify a purpose that would require modification of a project for which the build manager does not have permission to modify, the operation will fail.