The project manager initially creates a work plan in Project Management to perform planning and tracking activities. These activities include defining the project, scheduling tasks, and tracking actuals. The first time the project is synchronized, Project Management creates a new project file on the project manager's desktop computer. For each subsequent synchronization, all of the information in the Microsoft Project file is replaced with the current information in Project Management.
Even if you want to manage your work plan using Project Management, you can create it initially in Microsoft Project.
After synchronization, the project manager can distribute the Microsoft Project file or use it to run reports for managers and other people in the organization.