Yes, it is for the ability to use a large screen, as you would a normal desktop, but this is a device with a touch screen and a great, just because I'm using it as a desktop replacement doesn't mean I'd be willing to sacrifice the usability of the pen. I'd love to have documents and source material open on the desktop displays while having one note open on the surface for various thoughts etc as I'm ploughing through the work on the main monitor. No different to having a pen and paper at your desk.In my opinion, you get the dock to use your Surface as a desktop. When you make your Surface a desktop you very likely will attach a monitor of size to it. I can't see doing a much business work in the office using the Surface screen. It's great that you can carry your business computer on the road with you are to a meeting. With the Microsoft dock, you just pop the sides open and grab your Surface to take to a meeting or wherever.
I don't see the angle of the Surface as it sits in the dock as much of a detriment. Even the majority of my laptop users prefer to have a monitor connected to their laptop when in the office. I just setup one of my users (a director) with a Surface 3 i5 with two 22' dvi monitors. I set it up so the Surface monitor makes a 3rd display to the right side. I have doubts that it will come in to play much but I gave him the option.