Titles certainly aren't necessary for individual chapters. Plenty of great novels simply use numbered chapters to break the story into sections. Still, some novelists use chapter breaks as an opportunity to add clarity or another dimension to the unfolding story.
Russell Banks' The Sweet Hereafter is written using a series of first person narrators. Titling each chapter with the name of the narrator helps establish who is speaking.
In The Shipping News, Annie Proulx titled each chapter with a mariner's term along with a definition or description. For example, the third chapter is titled “Strangle Knot" and is followed by this description from The Ashley Book of Knots: “The strangle knot will hold a coil well . . . It is first tied loosely and then worked snug." The titles work in harmony with the book's setting—the Newfoundland coast—and the job of the main character, Quoyle, who reports the shipping news. Also, each title correlates with the action in the chapter. The chapter “Strangle Knot," for instance, chronicles the series of events that build in intensity, including Quoyle's parents' suicides, his wife's death, and the near loss of his children, ultimately motivating Quoyle to pack up his belongings and move his family to his ancestral home in Newfoundland. A strangle knot of a situation if ever there was one.
Marisha Pessl's Special Topics in Calamity Physics is structured as a literature course syllabus, which works in harmony with the brainy narrator, Blue van Meer. Each chapter is the title of a literary classic with which the events in the chapter have an association (some more sly than others). The chapter titled “Brave New World," for instance, includes a first day at school. The book culminates with a final exam, completing the syllabus structure.
So while titles are certainly not necessary—many novels don't have them—they have the potential to create unity or add another layer to the reading experience. If you use them, make sure they're contributing in a meaningful way. The reader will be looking for associations.
