If you are creating your own mind maps, you are remembering the connections as you go. It helps you associate terms with categories/topics and group items correctly . If you are looking at someone else’s mind map, that can be beneficial, but it’s likely not making the same lasting connections.
One great example is a person who decided to take the bar exam several years after attending law school. The bar is considered one of the more difficult exams one can take so he created a mind map of all his study material. When he was finished with the map/outline he took the bar and passed on his first try without any additional studying. The process of connecting the dots with visuals was enough for him to remember everything he needed to know to pass the bar.