Switching wp_get_sites to get_sites

This is a great question.

First of all, the comparison operator (?:) you’re referring to is called a ternary operator. It’s great for simple if/then blocks. It took me a while to get used to them, but now I use them all the time.

You can take a simple expression and return a value depending on the result of that expression.

This will put the sanitized value of $_GET['string'] into the variable if it exists, and an empty string if it does not.

$query_string = isset($_GET['string']) ? sanitize_text_field($_GET['string']) : '';

You can also echo this directly

echo $name != '' && isset($name) ? "Hello, " . $name : "I don't believe we've met"

Or put it in an array… and with booleans!

$my_array = array(
    'is_gt_5' => $this_number > 5 ? true : false
);

Why use them here?

The reason someone might use a fallback is because not everyone is on 4.6 yet. Writing it this way helps maintain backward and support future compatibility.