Lightness of tone helps disguise the brutality of the class system in England at the time. For example, Elizabeth's good-humored lightness in making a joke of Mr. Darcy not dancing with her disguises the reality that such snobbery had real-world consequences for people lower on the class ladder, who were excluded from access to privilege based on their birth. In fact, Austen deliberately uses Elizabeth's naive outlook and tendency to see the comic aspects in what is going on around her as the narrative point of view in order to soften the brutal aspects of the class system (while at the same time exposing them).
For example, what seems through Elizabeth's eyes to be the annoying buffoonery of Mr. Collins's framing his marriage proposal to her as doing her the favor of allowing her to maintain her class status after her father's death disguises the brutal reality that Elizabeth, her mother, and her sisters will be rudely cast out of their home with very little income and almost no respectable way to earn money if the daughters don't make good marriages. The comic treatment of Mrs. Bennet's obsessive matchmaking on behalf of her daughters also mutes the harsh reality of what awaits the women. Ridicule is cast on Mrs. Bennet by the embarrassed Elizabeth, but a more sober assessment might focus on the desperation that drives Mrs. Bennet.
Austen's comic portrayal of Lady de Bourgh as pompous and intrusive also disguises the way her money and status give her the right, in reality, if not in theory, to trample on the lives of those below her. We might laugh, too, at the servile deference Mr. Collins shows her, which Elizabeth finds ridiculous, but his actions reflect the reality that he understands that Lady Catherine's patronage is important to him: he keeps his job at her whim, not based on any objective criteria of competency as a preacher.
As W. D. Harding noted long ago in his essay "Regulated Hatred," Austen uses a lighthearted approach to expose a brutal class system. All of this might make us wonder how Elizabeth will exact payback once she has married Darcy and is at the top of the social heap, a subject Austen is silent about.