As we've both said before, you should understand and adhere to the basic rules of composition. You don't have to be a slave to those rules, but they exist for a reason. They were developed through the years to help you create a composition that is pleasing for your viewers.
Patterns and rhythms are powerful devices to help make your photographs grab the viewer's eye. The combination of similar shapes, lines, and even colors, in regular intervals, creates these patterns. You've seen natural patterns in flowers, water droplets, or rows on an ear of corn.
Man-made patterns are equally easy to find in buildings and the way we organize our lives. Whether these patterns are natural or man-made, they bring a photo together and impart a harmony of composition (how's that for artsy-fartsy?).
If you understand the concept, you can create a violation of the rule and drive your viewer's focus to an interruption of the pattern. The window in the shot below disrupts the pattern of the siding of the church. The leaf on the plums performs the same function.
As with all rules, once you've learned how to see and use them, you can try new combinations and have fun with all the possibilities.