Experienced dancers know that the body produces continuous lilts or cadences due to the alternate weight change 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 a baby being comfortably swayed in the cradle, or fish being gently surged by the wave, which is 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 directions. The man swings the woman's torso, causing her free leg to swing along. As that leg lands, he goes on to swing her torso in the opposite direction, resulting in her other leg to swing reversely. This is how ocho is made. However, the woman could take advantage of the inertia by swiveling her hips as her weight is sifting to the landing foot to let her other leg swing in roughly the same direction. This is how molinete is made. The cadencia used in ocho and molinete is essentially the same technique. (See Dissociation and Gear Effect.) Tango teachers usually do not emphasize the swing of the body when they teach ocho and molinete. But, if the cadencia is blended in, it will not only make the movement more elegant, outlining the beauty of her flexible body, but also produce a lilting feeling, making the dance 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 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 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 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.