I'm honestly not great with mind maps either, but it was a more fluid way to hold information. I actually redownloaded FreeMind and pulled up the old mindmaps - oh nostalgia.
One of them is to help keep track of character details and relations. Nodes were whether they were a main character, minor character, someone referenced in passing, and then the character name, and then a breakdown of details around them (family, special abilities). I think I also intended to include major plot points I wanted to hit as well, as I was big on planning at the time.
The second was going to take place in a made-up world, so that one has character details and also location details, so I could keep everything straight and have one document to reference to make sure I was being consistent.
Of course, neither of these ever got written, so take it how you will haha. I think the map was just more visually appealing than a list of these items, since related things can be linked easier than in a doc.