The body produces continuous lilt due to the alternate weight change from one foot to the other. The lilt can be enhanced by the push or pull of her torso with his torso to increase the motion of the body in accordance with the rhythm of the music. This technique is called cadencia. When the woman is led to do cadencia, it feels like the baby in the cradle being swayed, or fish in the water being driven by the waves, which is a cozy feeling for both but especially for the woman, as she is the one nestling in his arms and enjoying the ride. (See Cadencia.)
Cadencia is usually done alternately in the opposite directions. The man swing the woman's torso with a push or pull of his torso to bring her hip and leg to swing. As that leg lands on the floor and her weight is transferred to it she pivots and swivels her hips instantaneously to allow him to take advantage of the inertia to swing her other hip and leg in the opposite direction. This is how ocho is danced. Tango teachers often emphasize the swivel of the hips or dissociation but overlook the swing of the body or cadencia when they teach ocho. However, if the cadencia is blended in, it will not only increase the elegance of the movement but also produce a lilting feeling, making the ocho more enjoyable.
In order to do that there must be some speed or momentum. If you dance on the same spot without a horizontal motion, it would be difficult to generate the swing. That is why experienced dancers like to dance in the flow. When the floor is full of experienced dancers, you will see a counterclockwise flow of people like waves surging forward in correspondence with the rhythm of the music, and the speed of the flow is quite fast. But if there are too many novices on the dance floor, then the speed of the flow is slowed down. Sometimes it even becomes like a pool of stagnant water.
Novices who have no sense of flow often remain at the same spot doing steps, disregarding the people behind waiting for them to move on. (See Spot Dancing in Tango.) In an empty room that may cause no problem, but if you dance on a crowded floor, that could cause obstruction to traffic. Mark Word calls such people "rocks in the stream". You drive to work in the morning and suddenly there is a slow car blocking your way, that is the same feeling. People dancing on a crowded dance floor must not be such "rocks in the stream". I'm not saying that you may not slow down or pause for a moment and then move on. Experienced dancers do that also, but they do so only when there is enough space, or when the music tells everybody to slow down. If the people behind are approaching, then you need to move forward to avoid causing obstruction to traffic. This is the code, which everyone dancing on a crowded dance floor must follow.