>>325348420
It creates a fake bone at that point off the end of the bone. Unity only sees the beginning point of the bone and the direction it's facing. The length of the bone in blender is not transferred to unity so when it is trying to calculate physics on it, it's a one dimensional point. It has a length only if there is another bone child where it will draw a line between the two or an end length which gives it gives it a second point whatever distance and direction away you set. If you have a single bone (example: on a penis), you can add end length to make the dynamics actually work.