The id can be used to look up a particular message in the replica which supports various business logic

When Alice adds a message optimistically to her replica, she can simulate almost everything in the final result except the id .

The id is an important part of the message identity as it assigns uniqueness to each message in the replica collection. The id is also an important part of the view creation logic as it is used as the key in the React render function that maps an array of messages to JSX. […]