I'm way short of the definitive source, but section breaks and chapters do exactly what you said--break the work into manageable chunks. They're more common in the last twenty years or so, when so many people find their reading time coming in small increments. The writer makes sure there's a stopping place pretty often, since readers hate stopping mid-chapter.
Most of the time, the section break or chapter falls when certain conditions exist in the narrative:
--There's a gap or jump in time. Josie goes to sleep, end of section. Josie makes coffee, start of new section. (Boring book, though!)
--There's a change in setting. Elvin gets in his Corvette and heads for Vegas. Elvin slowly drives down The Strip. (Setting, remember, includes both place and time.) Or, Vanessa gets out her bike and pedals uncertainly toward the nearby village. In the village, she struggles to avoid vehicles.
--There's a change in point of view. Vanessa pedals toward the village. A bus driver worries about her son's failing grades and nearly collides with a young bicyclist who runs the stop sign.
--There's a small cliffhanger. Morrie hears--what is that, someone shouting? Damn it, he came here to de-stress. The sound nears his rented mountain cabin. Idiot hunters. Drunk, probably. Who else would be yelling in this peaceful setting? The door bursts open! (break) His landlord tells him he needs to evacuate, there's a fire approaching from the other side of the mountain.
If you're looking for fiction tips, you won't do better than AbsoluteWrite. (There are several other trans writers, too.)
P.S. This is how part of the alphabet would look if you eliminated Q and R