What literary technique is being used here, and for what purpose? Refer to the passage to support and explain your answer.
One other person had a part in the story of the cafe—he was the former husband of Miss Amelia, a terrible character who returned to town after a long term in the penitentiary, caused ruin, and went on his way again.
Whenever a character is described in a "story" of any kind (short story, play, novel, etc.), it is called "characterization."
Lilia Melani of Brooklyn College describes characterization as:
...the way an author presents characters. In direct presentation, a character is described by the author, the narrator or the other characters. In indirect presentation, a character's traits are revealed by action and speech.
The example you have provided would be direct presentation.
However, when you discover more details as to the character of Marvin Macy in reading, for example, of how he acts with Miss Amelia when they marry, or how returns many years after Miss Amelia has thrown him out, to then lure Cousin Lymon away, you possess indirect presentation of his character, where your sense of Macy is "filled out" by what he does and says in the story.
The purpose of providing characterization is that it allows the reader to better understand the character's place within the story; the characters drive the plot. You are also able to better comprehend the significance of the reactions of other characters to that person.
For example, knowing that Macy has been in jail, caused ruin, and then went on his way gives the reader a clearer image of Miss Amelia in several ways. We better understand why Miss Amelia would not have wanted Macy around, and why she would not have wanted a physical relationship with such a man.
This information allows us to also study Miss Amelia on a deeper, more personal level. For example, with the reputation Macy has before they marry, why would she marry him anyway? (Of course, we learn that she is lonely, and this generates a new sense of who Miss Amelia is, and also why Cousin Lymon becomes so important to her.)
It also gives the reader a clearer awareness of Miss Amelia's displeasure when Macy shows up, a sense of how she could have had a physical altercation (fight) with him, and how devastating his final act of aggression toward her is. Specifically, he influences Cousin Lymon and they destroy the cafe, and then Macy takes Lymon along when he leaves. The "wreckage" left behind is seen in Miss Amelia's total sense of abandonment and isolation.
In summary, the literary device described is characterization. The usefulness of this device is to provide an introduction to the character to explain his behaviors and to better understand the response of other characters to him based upon his how he acts and what he says.