You know the difference: the speaker who tediously repeats stuff (repetitious) vs. the one you mentally thank for going over the point again (repetition). Psychological studies show that a point can get lost without some repetition; but that too much is a turn off. The funny TV commercial that remains funny when moderately repeated can get really annoying and unfunny in excess. Eyes glaze over in court when the same question is asked and answered too many times, even if it was a good question. So advocates, persuaders and presenters have a fine line to draw and walk.
In visual art, repetition is an artful tool that’s used in many ways. One is to tie together a composition. Here’s an example in a stained glass window design by one of America’s greatest architects, Frank Lloyd Wright, at the Chicago Art Institute:
Wright’s design is filled with repeating shapes and colors (see how many you can count). The design works because the repetition is interesting rather than tedious, and ties together the composition into a whole theme. See the balloons, the 4th of July colors and the flag? Even though the repeating circles are flat, variation in diameter gives the balloons perspective—larger circles in foreground and smaller in distance.
Wright discovered that balance is the key to repetition versus repetitious. Said another way (to repeat!): repeat a point enough to tie the whole together, and then stop.