Mind maps help me realize things. I use a conference room whiteboard rather than an app.
Starting with asking a question as the root node like "Goals?" and then putting goals around that, and then from those goals, things I'd need to do to accomplish them. "Obligations?" and writing out various people/places/things I have obligations to, and then next what it means to fulfill those obligations.
Being able to look at it all on the whiteboard and pace around a bit seems to be very useful for me. This type of thing helps me sort things out and frequently I have realizations during it that make things more clear.
I mostly do project planning in outlines, but sometimes I will break out the whiteboard. Sometimes those are mind maps and will make me see missing pieces; frequently, I suppose they're diagrams and may not count.