Use of unset in PHP

If we declare any variable as unset then it will be undefined for the next part of the coding. See example :-

<?php
echo "<center>";

$a="Mahi";
$b="Piyu";
$c="Bhavna";

echo $a." ".$b." ".$c."<br/>";

unset($a,$b,$c);

echo $a;
echo $b;
echo $c;

echo "</center>";
?>

Output:-