Option to more densely pack branches
When creating large mindmaps it would be nice to have an option to more densely pack nodes/branches together to save space (see screenshot, branch in centre of screen could be much closer to branches above and below it. My map is using the To right node layout.)

This is not a bad idea; however, the implementation of this compared to the current implementation would be fairly complex. Not a feature that I would place high on my priority list of features to implement.
Though not nearly as convenient, if you want to achieve a higher level of packing, you could always use the manual node placement layout option. In this layout configuration, adding new nodes will follow the same layout as any of the other layouts, but you can then drag nodes around to any location required. The node's descendents will follow the parent node when being dragged, so it's a little less cumbersome than having to manually drag around all nodes.