often misunderstood, this is an internal break within the chapter required for a major scene shift, but particularly when the Point of View changes from one character to another (another major scene change). POV rules apply most strictly in 3rd person limited story mode, where the narrator is limited to only one character point of view at a time and other character's most reveal their intentions and development through dialog and action (and other narrating devices, such as probability assumptions). The section break, in its loosest manifestation, is signaled by three carriage returns, but most often is represented by three asterisks centered at the break ( * * *). More formally (my preference) is a number sequence (1,2,3 etc) for each section break. Even if the POV switches for one paragraph or one sentence, the section break should be observed.
Edward C. Patterson