Changing the status of your project can have two effects: it can restrict who can send invitations to the project, and it can restrict who can add content to the project. There are four possible project statuses:

Normal: Every member of your project can invite others. This is the standard way projects are run as it encourages members to bring in other people and typically, the more the merrier!  

Managed: Only YOU, the project organizer, can invite others. When someone joins the project, they can add their stories and pictures freely, but they can't invite others. Sometimes this is desirable when you want to closely control who is invited and able to participate.

Restricted: This status is handy when you're ready to finalize your book before ordering and don't want any more surprises. In "Restricted" status, only you are able to continue adding and editing content in the project. Other members of the project will still be able to see all the pictures and stories, but will not be able to add more content or change what they've already written.

Closed: A "Closed" project takes things a step further and disables all features to add stories and pictures—even for you.  (Keep in mind these settings aren't permanent. You can always update the status of a project from "Closed" back to "Normal" if you want to).