The game development paths winds through the unknown on a continous basis. And a core component for effectively handling the unknown requires updating one's mental model and pushing the edge of understanding.
An old Indian parable describes how 3 blind men, holding each part of an elephant are convinced that they have 3 different animals.
Mindmaps, in my experience, offer a holisitic and methodical approach for mapping out what's at the edge of one's understanding: They capture what you know, and perhaps more importantly, reveal the empty space of what you yet don't know.
Below is an index to the current mental maps that guide me about the elephant: