For starters, the human attention span does have limits, and so chapter breaks are handy ways to allow the reader to pause if he wants to step away from the story with a temporary sense of completion. While it might seem inconsequential, it is actually vitally important for maintaining reader interest over the long haul of a novel. So there is a practical element to having chapter breaks.
How you organize the elements of the story into those breaks is actually a creative decision. Some stories are told with chapter breaks every couple of pages (or even more frequently). This constantly repeating use of breaks actually contributes (or detracts if mishandled) from the overarching story or message of the book itself. Frequent chapter breaks can connote a sense of panic, or lack of attention, or any number of things.
Conversely, long chapters with infrequent breaks can connote a sense of slowness or preference for the methodical, and this will be successful if it makes sense within the context of the story being told.
Many times, chapter breaks occur naturally around known life events, such as the end of a wedding party, or at a graveyard after the casket is lowered, or in the hospital after a baby is handed to her mother. Other times chapter breaks are intentionally inserted in the middle of the action, and lead to other chapters that are picking up after an abrupt ending.
Again, breaking your content into chapters should be done on the basis of alignment with the overall tone of the story and used as a pacing mechanism.