I know your question was directed to
Gordon...but I use mindmaps quite a
bit...
Here is the theory( what happens in real
life is another issue)
Supposedly the map is used to keep generating
ideas(all the branches) and you just keep
generating until WHALA! you're suppose to
see a way you can use the information. You
might end up in the final product only using
part of the mind map or just a few branches.

The theory is to use it as a organizing tool
and idea generator and then to get a aha
experience on how to put together a project.
I have found the Mindmap is not always useful
on all projects and in some cases I'm better
off using a generic outline. The mindmap helps
me when there are so many issues I'm not sure
where to begin my final project...
this is just my .02 perhaps Gordon will give
you the "dollar"...;-)