Changing Importance:

Red herrings are designed to make something appear more or less important than it really is. Several good examples of this technique can be found in the motion picture The Fugitive. In one scene a police car flashes its lights and siren at Dr. Kimble, but only to tell him to move along. In another scene, Kimble is in his apartment when an entire battalion of police show up with sirens blazing and guns drawn. It turns out they were really after the son of his landlord and had no interest in him at all. Red herrings can inject storytelling tension where more structurally related weaving may be lethargic. (Note the difference from changing size, which concentrates on the changing extent of something, rather than re-evaluations of its power.)

From the Dramatica Theory Book