NED12 Rhythm and flow

Rhythm is a pattern created by repeating or varying elements, with consideration given to the space between them, to create an effective ebb and flow which visually leads the eye from one element to another.

From WikiBooks:

..human beings are more comfortable with variation in general. Psychologically, most any serious lack in variation of anything (a solid, a line, a sound, a situation) can become very boring. Adding a little variation at non-specific intervals (every now and again) gives most any design an interesting appeal as long as it is not overdone.

If rhythm is overdone it can be disruptive and create a counter-dynamic.