You have to make sure that you have all the little parts you need to make your big parts, and enough of the big parts to build whatever it is you ship. You need storage space, shipping and receiving capability, inventory tracking systems, and people to manage it all.
Software companies have much less of an inventory problem, at least in the traditional sense.
What we ship to customers is just a CD and some paper. It's cheap and easy to manufacture, once you have the master CD and the proofs for printed materials, and there's no problem with long turnaround times and no need for huge warehouse space. Our REAL equivalent to the inventory process is tracking all of the elements that go on to that master disk. We start with source code. With the help of CVS, we can all do our programming work without worrying about what other programmers are working on, which is a great time saver.