Experienced dancers know that the body produces continuous lilts or cadences due to the alternate weight shift from one foot to the other, which can be enhanced by increasing the motion of the body. (See Cadencia.) When the dancers swing together in rhythm to the music, it feels like the baby in the cradle being comfortably swayed, or the fish in the water being gently surged by the wave. It's a cozy feeling especially for the woman, as she is the one nestling in his arms and enjoying the ride. (See Driving and Synchronization.)
The swing usually alternates in opposite directions. The man swings the woman's torso, causing her free leg to swing along. As her foot lands, he goes on to swing her torso in the opposite direction, resulting in her other leg to swing reversely. But, the woman could swivel her hips as her weight is shifting to the landing foot, so her free leg could take advantage of the inertia to swing in roughly the same direction. This is how molinete and ocho often being danced. The cadencia used in molinete, front ocho and back ocho is essentially the same technique. (See Dissociation and Gear Effect.) Tango teachers usually do not emphasize the swing of the body when they teach molinete and ocho. However, if the cadencia is blended in, it will not only make the movement more elegant, outlining the beauty of her soft and flexible body, but also produce a lilting feeling, making the step more enjoyable.
To generate the swing, there must be some speed in the horizontal direction. If you stay at the same spot doing steps without a forward or 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 such dancers, you will see the flow of people moving counterclockwise like the waves surging forward in accordance 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 place doing steps, disregarding the people behind waiting for them to move. (See Spot Dancing in Tango.) In an empty room this may cause no problem, but on a crowded floor that is senseless. 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 kind of feeling. People dancing on a crowded dance floor must not be such "rocks in the stream". I'm not saying that you cannot slow down, pause for a moment, and then move on. Veterans dance in slow motion as well. But they do so only when the music tells everyone to slow down, or when there is enough space. 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.