Well, you can take out the laptop without disconnecting all your cables.Originally Posted by bimmerpc
Some docks provide more functionality. (Additional PCI slots, SCSI, etc)
I can't think of anything that you couldn't do to the dock instead of the laptop (power button, etc). Though some of the generic USB ones, don't imagine they actually have a power button (but I could be wrong). So if it doesn't have a power button, you still need to address power on.
Wether it's worthwhile or not from a cost perspective, depends on what your options are for docking your system.