In Chapter 37, David tells Dora that Aunt Betsey has lost her fortune and that he now needs to work for money. Dora reacts badly, and Dickens emphasizes her bad reaction with a hyperbole:
At first Miss Mills thought it was a quarrel, and that we were verging on the Desert of Sahara; but she soon found out how matters stood, for my dear affectionate little Dora, embracing her, began exclaiming that I was ‘a poor laborer;’ and then cried for me, and embraced me, and asked me would I let her give me all her money to keep, and then fell on Miss Mills’s neck, sobbing as if her tender heart were broken.
It is unclear whether Dora herself is exaggerating when she calls David a "poor laborer." This is certainly not what David told her, but it is possible she really believes it. The narrator, on the other hand, carefully chooses to emphasize Dora's language as hyperbole. Rather than recounting the conversation word for word, he summarizes most of what Dora says but directly quotes "a poor laborer" because he wants the exaggerated ridiculousness of this statement to stand out.
The stance of the novel is that it will be good for David to work to support himself. It may not be ideal for Aunt Betsey to have lost her money, but David has developed a new kind of energy and drive through knowing that he does not have this cushion to fall back on. Dora, on the other hand, loses all composure at the idea. If she really believes he is a poor laborer, it goes to show not only how sheltered she is, but also what an old-fashioned view of the world she has. Dora seems to think that people are either rich enough never to work, or they are "poor laborers." In the middle-class world where David wants to succeed, there are many classes between the poor and the aristocratic. In fact, Dickens's novel seeks to elevate a middle class that values labor as a character-building endeavor, not just a means to survival. The hyperbole emphasizes what a bad match Dora is for David in the context of the Bildungsroman. Dora's view of success, which involves wealth without labor, is fundamentally incompatible with the ethos David is supposed to be cultivating.
In Chapter 49, Mr. Micawber bursts into tears at Miss Betsey's. He uses a string of hyperboles to describe his newfound determination to expose Uriah Heep as a liar and cheat:
[...] I’ll know nobody—and—a—say nothing—and—a—live nowhere—until I have crushed—to—a—undiscoverable atoms—the—transcendent and immortal hypocrite and perjurer—HEEP!
Even if Micawber meant to murder Uriah Heep in retaliation for what he has done, the idea that he could "crush" him into "undiscoverable atoms" is clearly an exaggeration. It would not even be possible. But because Uriah is a "transcendent and immortal hypocrite and perjurer" (another hyperbole, meaning that he goes beyond the scope of what seems humanly possible as a hypocrite and liar), Micawber wants a transcendent and permanent way of getting back at him. This claim is the last of many wild exaggerations. It goes beyond the realm of possibility to convey the intensity of the vendetta Micawber has built against Uriah.
Micawber and Dickens both mean for the outburst to be shocking and to make everyone wonder what Uriah Heep could possibly have done. Micawber, though sometimes foolish, has generally been good-natured. The fact that he is resorting to such violent language indicates that whatever Uriah has done is bad enough to alter Micawber's character. David has long suspected Uriah of corrupting Mr. Wickfield's character. One of the worst parts of his villainy is that he is like a black hole, sucking others into his orbit and altering the way they behave. Micawber's hyperbole is violent and goes beyond the realm of possibility, but it also seems like a fitting way to deal with Uriah. Shattering him into "undiscoverable atoms" would prevent others from being drawn to him and his villainy.