PDO パスワードのハッシュ化によりコードのセキュリティはどのように向上しますか?

$sql = "SELECT * FROM users WHERE username = :u";
$query = $dbh->prepare($sql); // prepare
$params = array(":u" => $_POST['username']);
$query->execute($params); // execute

$results = $query->fetchAll(); // then fetch

if (count($results) > 0) {
    $firstrow = $results[0];
    $providedPassword = $_POST['password'];
    $hashedPasswordFromDB = $firstrow['password'];

    if (password_verify($providedPassword, $hashedPasswordFromDB)) {
        // Valid login
    } else {
        // Invalid password
    }
} else {
    // Invalid username
}

$dbh = new PDO(...);

$username = $_POST["username"];
$email = $_POST["email"];
$password = $_POST["password"];
$hash = password_hash($password, PASSWORD_DEFAULT);

$stmt = $dbh->prepare("insert into users set username=?, email=?, password=?");
$result = $stmt->execute([$username, $email, $hash]);