It's the only reason I switched my more complex software to 5.10 from 5.8 minimum requirement. It alleviates doing stuff like:

sub func {
    my ($thing) = @_;
    $thing = defined $thing ? $thing : 'non-thing';

    # or

    if (defined $thing){
        $thing = $thing;
    }
    else {
        $thing = 'non-thing';
    }
}
[download]

Much cleaner to use the previously-mentioned defined-or:

sub func {
    my ($thing) = @_;
    $thing //= 'non-thing';
}
[download]

That might not look like much of a difference, but add some complexity and other rules surrounding incoming variables and you can significantly reduce the keystrokes, code complexity and most important, readability, especially if in loop-type scenarios.