Think of how you 'load' a fishing rod. You don't swing it back, stop, and then swing it forward toward the water.
As you are swinging the rod back, you then 'shift' directions - this change of direction is what bends the rod. See what happens when you swing the rod back and come to a complete stop. You've removed a lot of the dynamics.
Good players probably don't think about the transition, but it's a feel to them. Some my feel it in their hands and shoulders. For others it's in the feet and legs.
I believe Brian elaborates on the transitions in the Soft Draw video with the 'back and forth' drill. Before you swing down, it's important to be well settled into your left side. That is to say the weight is gathered on the left foot (or left instep) before the back swing is completed. Keep in mind that the golf swing takes place in like 2 seconds, so it's going to seem like everything happens at once.
Perhaps another facet to this discussion is the 'start down' move which might be another name for transition.
What do good players do as they are finishing their backswing? To me, there is no more important move in the swing then what/where the body is doing at this critical moment.
Erik