It allows you to move the computer to your data. There are lots of places where power can be an issue (solar collection only), a full 'computer' would take up a lot of power and space. A micro like this would allow you to process signals on site and only send back 'important' information over potentially limited bandwidth. The device is inexpensive and generic, so you can program it do to what you need, there are many custom devices that do what this board can, but they are either expensive or fixed function.
Not only that. Imagine tying a ton of these together, with a hundred of them, say, you would spend as little as ~9k and have a supercomputer on your hands. Or, suppose you want to create some sort of small device that relies on existing software like an MP3 player or some sort of video player. This would allow you to build it, without a lot of trouble having to do things from scratch. Or this could power a laptop sans screen... it goes on and on.
I'm a designer who also programs, so don't fully understand why this is cool. Can someone explain?