Generally speaking, the goal of the document is to communicate the game design to all the parties involved in game development. But it's very unlikely that the whole design is going to be covered by a single document. Some parts of the game might need to be designed as soon as possible, while others might wait for a later stage or even need to be designed after some of the features have been implemented.
A development team can reach over 200 people in AAA productions and many people will have a very specific role. Imagine if a programmer in charge of developing the multiplayer network was forced to read a 1,000-page document to understand what they needs. They will get information about levels, characters, storyline, or the ...
