This device makes it easier to work with many peripherals at home and still makes it easier to disconnect when you want to go portable. Think of it as a docking station.
"The ThinkPad Port Replicator II provides easy cable management and one-step connection to desktop accessories at home or in the office. It offers pass-through connection for Gigabit Ethernet, USB 2.0, and DVI, as well as standard ThinkPad notebook ports. An integrated system tray provides a stable fit and comfortable typing angle. One easy step eliminates the hassle of connecting multiple devices one-by-one to the ports on the ThinkPad system.
Pass-through (replication) of ThinkPad notebook ports including: Gigabit ethernet (RJ-45), including modem (RJ-11), USB 2.0, DVI, VGA, serial, parallel, PS2-keyboard, PS2-mouse, diskette drive, audio line-in and line-out Gigabit Ethernet pass-through port (will function as 10/100 ethernet port for system without gigabit ethernet) USB 2.0 pass-through port (will function as USB 1.1 port for system with USB 1.1) On/Off switch - System can be powered on/off using the button on the ThinkPad Port Replicator II Includes a slot for an optional cable lock Power pass-through -- use the AC power adapter that ships with your ThinkPad or with an optional power adapter Compatible with X20/21/22/23/24/30/31, T20/21/22/23/30/40/41/42, R30/31/32/40/50/50p/51, and A20/21/21e/22/22e/30/31 (Does not support X40/41, R40e/50e, or G40)"