why use isrequired in proptypes code example

Example 1: proptypes array of objects

MyComponent.propTypes = {
  items: PropTypes.arrayOf(
    PropTypes.shape({
      code: PropTypes.string,
      id: PropTypes.number,
    })
  ),
};

Example 2: proptypes.objectof

Pokemon.propTypes = {
  pokemon: PropTypes.shape({
    name: PropTypes.string,
    id: PropTypes.number,
    base_stamina: PropTypes.number,
    base_defense: PropTypes.number
  })
}