Not that late-night visits would seem any more innocent, but for some reason acts of this kind felt more appropriate when performed after the fall of darkness.
-- Narrator (Part 1: Chapter 1)

Importance: The reader understands from this sentence that Sara is having an extra-marital affair with the man whom she meets. The fact that she meets him in the middle of the day, with her young son in the car, is highly inappropriate for the visit that she is having.

Harry had never had any use for this on the job and only once for the other thing he had learned over there: how to catch a serial killer.
-- Narrator (Part 1: Chapter 2)

Importance: It was when Harry took an FBI course in Chicago that he learned a technique for speed handcuffing. He considers the class almost useless because he has never had to use this speed handcuffing techniques and has only once caught a serial killer, another topic of...