Essentially they are all about creating a breadth-first outlay, when there are lots of things to cover, think about, or discuss. Then you can tack your additional needs on around that.
Tony was also obsessed with learning, memory, and memorization as general aims in life, so he tried to map natural patterns like sensory factors, fractals, and meaningful branches onto his mind map scheme. In his view, this merge with the mystically-natural was in effect a merge with the best one could achieve in taking notes.
IMHO however, those are some of the least interesting parts in terms of day to day note taking utility, and the capture of a broad set of ideas as if it's all owned by one central topic is basically fantastic enough for most uses. This is also known as a concept map.
I often see these mind map things and I'm interested in learning what benefits they can provide me, but I have no idea how they're actually used. My searches have only yielded people using them as study aids.