client/extensions/woocommerce/state/sites/settings/mailchimp/reducer.js
function saveSettings( state = false, { type } ) {
	switch ( type ) {
		case WOOCOMMERCE_MAILCHIMP_SAVE_SETTINGS:
			return true;
		case WOOCOMMERCE_MAILCHIMP_NEWSLETTER_SETTINGS_SUBMIT_SUCCESS:
		case WOOCOMMERCE_MAILCHIMP_NEWSLETTER_SETTINGS_SUBMIT_FAILURE:
			return false;
	}

	return state;
}
function saveSettings( state = false, { type } ) {
	switch ( type ) {
		case WOOCOMMERCE_MAILCHIMP_SAVE_SETTINGS:
			return true;
		case WOOCOMMERCE_MAILCHIMP_NEWSLETTER_SETTINGS_SUBMIT_SUCCESS:
		case WOOCOMMERCE_MAILCHIMP_NEWSLETTER_SETTINGS_SUBMIT_FAILURE:
			return false;
	}

	return state;
}
Updates state with save settings request status
The name ( saveSettings ) is generic because in future this should repond
also to other events than newsletter settings

@param  {Object} state  Current state
@param  {Object} action Action
@return {Object}        Updated state