Default behavior of UAC, even for administrative accounts, is to prompt the Yes/No dialog box, but not force the user to re-enter credentials. By configuring this GPO setting, you can additionally require that even admin accounts will have to re-punch their password before getting through a UAC prompt. Or, you can see here that you could alternatively Elevate without prompting, which squashes the UAC prompt and lets you make system admin changes without having to pass through UAC. Be careful here! While convenient, this is not a generally recommended way to go.