This Intro to Character Keys for 3D Printing video will go over the basics of making a Key in ZBrush. This Key can then be used and applied to any character or other model that needs to be broken up and printed as separate pieces. Parting out characters is a great way to print out characters larger than your maximum build volume, use fewer support structures and prepare for possible cast/molding.
This technique was used on my Stoick print to break out the arms in particular. I also did one extra trick where I also subtracted the arm shape from the armband so the bicep would inset with a key. This also made the connection nearly invisible. Anytime you can hide the attachment point the better off you are!
You can see on the left that the arm and armband join together seamlessly. With a little filler epoxy the final look will be pretty killer.