This feature is available to Business subscribers only. It allows other people to edit your project.
By default, only you can edit your projects.
When you want somebody else to help you, check the "collaborative editing mode" option, just like you do in Google Docs.
By checking this box you allow anyone with the link to view and Edit your project.
Your party will have full access to the content of the project but won't be able to publish it. You are the owner and only you decide what to publish.
Uncheck this option to make the project private again.