Smartfish,
Mind maps achieve two distinct, yet synergistic, objectives:
1. Mind maps facilitate RECALL by collecting several pieces of auditory information into fewer chunks of visual information. By doing so, you have an easier time recalling more pieces of information by visualizing one representative piece.
2. Mind maps facilitate COMPREHENSION by enabling you to understand how all the many pieces relate to each other within a larger perspective. By doing so, you begin to see a broader purpose for inclusion of the smaller bits in the author's work.
If you understand both of those reasons for mind mapping then you can more easily decide when the most beneficial time to mind map would be.
Good luck, and
CommonSense