why do we write useeffect in react code example

Example: how to use useeffect

import React, { useState, useEffect } from 'react';
function Example() {
  const [count, setCount] = useState(0);

  // Similar to componentDidMount and componentDidUpdate:  
  useEffect(() => {    
  	// Update the document title using the browser API    
  	document.title = `You clicked ${count} times`;  
  });
  
  return (
    

      
You clicked {count} times
       setCount(count + 1)}>
        Click me
      
    
  );
}