When using Fusion, the users can decide where they want to end up. For example, if one half was about to get crushed by a rock, and the other half was nearby, they could fuse to avoid an attack, as the half in danger would fuse to the place where the one not in danger is. Just like the Fission, Fusion can be used to dodge attacks, as it can be done at will quickly. It doesn't take that much time to activate.