What is the difference between -X (ForwardX11) and -Y (Forward11Trusted) options for SSH on Red Hat Enterprise Linux 4?

The -Y (ForwardX11Trusted) option:
With this option, remote clients are given full access to the X11 display - the remote clients are trusted. This option should be used with care and gives users the ability to bypass file permissions on the remote machine. For example, an attacker that had gained root on the remote box, gains the ability to access and effect the conte...