A project manager should consider carefully who is able to change the project plan.
You can specify the people who can change the product plan based on their roles in the project. Only users with the role you select can view, create, modify, and delete artifacts in the planning folder hierarchy, and populate those artifacts with content.
Every project must strike its own unique balance between openness and control. These broad guidelines may help you decide how to set up the appropriate roles for your project.
However, occasionally you may want to hide all or part of the planning folder hierarchy from selected people. For example, when you bring on a contract developer for a short period, you may want to restrict that person's view to the specific artifacts they are working on directly.
However, it may make sense to allow some people with a direct stake in the project to modify some folders. For example, if you are working with a product owner, it might be useful for that person to be assigning artifacts to future planning folders while your team is working on the current one.