I was a pretty avid reader growing up and I think I just kinda noticed them. And I used to get a little confused when my teachers kept knocking me for "run-on" sentences, when the books I read often had long-structured sentences.

Commas, semicolons, ellipses, em dashes, colons, parentheses — sprinkle them about and you can have a paragraph of a sentence (with side thoughts), and kinda do whatever you want... it's all about using "voice" through written word. (Period)