Mr. John Smith, shares some good points, but IMHO the main reason is that its running Linux!
Far, far more feature rich and stable than anything currently out there for embedded. Many things that would take you hours to code is probably a simple apt-get install away from doing it.
So many language programming options to choose from like c/c++, node, python and more. Pick you poison and start coding.
Unlike what we are used to in our embedded world, where say we need to make something that needs wifi. Typically you either code your own driver for it, or they have one for another product they sell. Which then you stuck using only that wifi module, and most of the time it's either not full featured, and or somewhat buggy or slow. Not the case with Linux, most of the off the shelf USB wifi devices at your local store will work just by simply plugging it in. In the rare cases it doesn't, most of the time you just install the drivers for it. Think of Embedded Linux like your PC, Most of the stuff you buy you just plug it in and it works.
I started to learn embedded Linux some months ago, but with what I have learned and tried so far I am convinced that much of the Embedded world is going to switch to products like this. The time savings for competing a project far exceeds just about anything else out there.
IMHO, today most of the companies that make these embedded Linux modules, just don't get it yet. They throw every dam connector on the board. That is great if your making a kit, but most of us are going to "embed" it into our product and need to have connectors in certain places and/or not have connectors. There are those out there like Gumstick and so on that don't do this but the modules is far to expensive.
This is why I am very glad GHI has picked this up, and offered it in a sensible form factor. Though I differ from Mr. John Smith is one aspect and that is I would have preferred a module with some form of SM header option so I can remove or install the module should I need to. Something along the lines of say the Intel Edison connector.