Basically be a lot more precise and accurate with any type of machining that I've been doing on my drill press or by hand. It'll also be nice to be able to provide ventilation other than hundreds of holes in panels that didn't come that way (say, from Context or Lansing) and also do more in the way of custom chassis fab from the ground up simply by buying the raw materials and making it soup to nuts. The mill coupled with the lathe should also open up a world of potential with knobs, shaft couplers, tube rings, etc. I don't expect to be using this stuff all the time or even a ton but what I wanted was stuff that when I went to use it wasn't fighting me half the time. The huge lathe that I have now (Craftsman 48") is just way bigger than I need and not at all suited for the type of small scale work (grado cups) that I've used it for 90% of the time. And the drill press is great for hole, but hard to hold work pieces in place with and not particularly good at working with metal in general. So the mill, for me, will most often just be a fancy drill press with a huge x-y table.
Oh and I figure from time to time I can bang out a few custom parts for you yahoos around here too.