what does ob_start do in php code example

Example 1: why use ob_start() in php

//why use ob_start() in php

<?php
ob_start(); //Start remembering everything that would normally be outputted, but don't quite do anything with it yet
$output = ob_get_contents(); //Gives whatever has been "saved"
ob_end_clean(); //Stops saving things and discards whatever was saved
ob_flush(); //Stops saving and outputs it all at once

?>

Example 2: ob_start in php

ob_start(); //Start remembering everything that would normally be outputted, but don't quite do anything with it yet
$output = ob_get_contents(); //Gives whatever has been "saved"
ob_end_clean(); //Stops saving things and discards whatever was saved
ob_flush(); //Stops saving and outputs it all at once