A chapter is a useful tool for the writer. It divides the novel up into easily manageable sections so the writer can spread the labour of writing the darn thing. It makes it easy to plan a book - say, three scenes per chapter of about 1500 -2000 words each scene, and twenty scenes - and there you are. Novel written.
Except it's not that easy. A chapter is not a useful tool for good story telling. A chapter is not a useful tool for rewriting. A chapter is not a useful tool for rearranging. Okay, I'm going to go headlong against those who like to plan out their novel before they start writing, but in my opinion a chapter is not a useful tool for writing a novel that works.
Writing by chapters inhibits creativity by arranging it into nice chunks. It's the Tick Box approach to writing, no deviations allowed. I've heard writers say that they couldn't possibly move this scene some place else, even though they can see why it's been suggested, because then the chapter would be too short. And rewriting is often out because it upsets chapter balance. And the amazing cliff-hanger which will have the readers turning the pages faster than a Zeotrope machine can't possibly go there because it is ordained that the chapter finishes six pages later on.
Sectioning the novel into chapters is about the last thing I do before it goes off to my editor. They may be between 1000-6000 words, but I'm looking for variety in length and brilliant chapter ends. As the novel gets towards the end, the chapters become shorter to help pick up the pace. Above all, the chapters go where it suits the story-telling and not the other way around.