Créer une entrée contrôlée:is it "value" really necessary with "input" in this case?

hello,
Créer une entrée contrôlée

in this ligne, is it “value” really necessary with “input” in this case ?:

<input value={this.state.input} onChange={this.handleChange}/>

because when I made the exercice I didn’t put th value property and the code worked. :thinking:

because for me but maybe I’m wrong, onChange() check the input, if there is a changing it send the “event” to handleChange() which send the new input’s value to the input of “state”.
So I wonder why value property is necessary here?
As I said, the code works without it.

class MyForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      input: '',
      submit: ''
    };
    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
         //   3
  }
  handleChange(event) {  // 1
    this.setState({
      input: event.target.value
    });
  }
  handleSubmit(event) {   // 1
    // Change code below this line
    event.preventDefault(); //  voir la note de l'exo
    this.setState({
      submit: this.state.input
    });
    // Change code above this line
  }
  render() {
    return (
      <div>
        <form onSubmit={this.handleSubmit}> // 2
          {/* Change code below this line */}
          <input value={this.state.input} onChange={this.handleChange}/> // 2
          {/* Change code above this line */}
          <button type='submit'>Submit!</button>
        </form>
        {/* Change code below this line */}
          <h1>{this.state.submit}</h1>  //4
        {/* Change code above this line */}
      </div>
    );
  }
}

Without value that’ll be an uncontrolled component, but the exercise is about creating a controlled component. In this particular case they’ll work identically.
https://reactjs.org/docs/uncontrolled-components.html
https://reactjs.org/docs/forms.html#controlled-components