Generator syntax for PHP

I just read through an example tutorial on using yield, and I have to say that I didn't understand it at all. I ran the example code, and it doesn't look like it's doing anything a regular forloop isn't able to do. It just iterate the numbers 1,2,3 like a regular forloop would do, except it's using a generator to do it? I don't understand at all, so if anyone can, please explain to me the differences between using a generator and a regular forloop.

function gen_one_to_three() {
    for ($i = 1; $i <= 3; $i++) {
        // Note that $i is preserved between yields.
        yield $i;
    }
}


$generator = gen_one_to_three();
foreach ($generator as $value) {
    echo "$value\n";
}
?>

Results:

1
2
3

Using just a forloop:

for ($i = 1; $i <= 3; $i++) {
echo $i;
}

Results:

1
2
3