suppose there is a set of linux machines on our intranet all in X desktops ( GNOME, KDE etc..) and if you need to call desktop of machine1 from machine2 it can be reached pretty easy with out any third party tools
1. Connect to the machine u want using ssh -x  user@server
now on the upcoming xterm u may start GNOME using
]#gnome-session
and KDE with
]#startkde



