A special feature is that you can share your book with family and friends. You can give them reading rights, so they can watch your book being created and read along.
Or you can also give them writing rights. This allows them to ask you questions, as well as answer questions when you're writing a shared book (such as the relationship book or the memory book).
Also use the feature when you are writing a memory book with many friends or with your family to remember a loved one.