I think the change in emphasis is important – many people seem to attack zenchu by throwing their heads at the ground, but you get better results when you focus on creating upward momentum first and rotation second.

The same is true of bakuchu, I think. Beginners often attempt to flip over too soon, so they have to rely on speed and end up landing poorly. Really nice back flips usually don’t rotate until closer to the jump’s apex. This allows a higher jump and gives more time for full rotation.