Although it is possible for good programmers to just think for a while and start programming right away, there is great value in having a design document before any code is created.

Think of this document as the blueprints of a house. Without that blueprint, the house will probably also have a foundation, walls and a roof, but the internal orientation of rooms, power and water connections and position of doors and windows won’t be optimal.
This blueprint affects how the structure of the house will be, before it’s built. In the same way, the design document affects the code of the program. Note that I’m not only talking about how the interface will look to the user (this is described in user-interface design documents, which are a part of the design document, but not all of it) but also how it will behave, feel, …

So what are the benefits?
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