switching to mysqli_prepared statements

I want to switch to mysqli_prepared statements but have a question before I start.

example 1

$query = $mysqli->prepare('SELECT * FROM users WHERE username = ?');
$query->bind_param('s', $_GET['username']);
$query->execute();

example 2

$query = $mysqli->prepare("SELECT * FROM users WHERE username = 'Rick' ");
$query->execute();

Is bind_param always necessary and why, for security reasons?