Segregate applications. If app one gets compromised, app two is off in another land. If my linode box gets hacked, without containers, all 16 websites will be compromised/go down.

Desktop virtualization using the NX protocol and Linux containers is also really friendly. Our company uses old Pentium D boxes for desktops. The performance gain from using a thin client + lxc + lubuntu is insane! I can actually watch youtube videos and draw in OpenOffice Writer. (Also great for disaster recovery scenarios).