Why use Upper-Bounded Wildcards if it can't be used

Question

I don't understand why/when we should use Upper-Bounded Wildcards since you can not use it. Here is an example :

import java.util.ArrayList;
import java.util.List;

public class Test {

    static class Parent { }
    static class Child extends Parent { }

    public static void main(String[] args) {
        List<? extends Parent> family = new ArrayList<>();
        family.add(new Child()); // 1. Doesn't compile
        family.add(new Parent()); // 2. Doesn't compile

        // List<Parent> parents = new ArrayList<>();
        // List<Child> childs = new ArrayList<>();
        // parents.add(new Child()); // 3. Compile fine
        // childs.add(new Parent()); // 4. Doesn't compile
    }
}

The point 1 and 2 doesn't compile. From what I have understood this will not compile because List<? extends Parent> can be List<Parent> or List<Child>, and since you can not for instance add a Parent instance in a List, Java prevent us of doing this and gives a compilation error. So my question is what's the point in using Upper-Bounded Wildcards??