The whole state is immune so it is not possible to handle state change locally in a sub-component. The parent component that embeds it needs to call it and plac

The whole state is immune so it is not possible to handle state change locally in a sub-component. The parent component that embeds it needs to call it and place a new updated component state into a new whole state. But then the parent needs to know which events go into the component. The messages nicely allow for that. Besides already mentioned ability to serialize messages it also allows to preprocess or filter messages in the parent.