Both the Tasks Center in PWA and calendar appointments in Outlook (with the support of the Outlook integration add-in) serve as timesheets for resources to report progress on their assignments.
The Updates Center in PWA allows project managers to evaluate, approve, or reject task change submissions from resources. Approved task changes cause Project Server to update the affected project plans in Project Professional.
The Project Center in PWA enables executives and other stakeholders to view project status across the organization and drill into the project plans that most interest them.