A setting is the place and time in which a text takes place. A plot are the events which makes up the action depicted in a text.
Therefore, the setting of a text has a profound impact upon the plot of a text.
For example, when reading a text about the South, one can picture things which may happen during a certain period of time. Texts such as To Kill a Mockingbird and Huck Finn are depicted as happening in the South. Therefore, the reader can relate to the fact of the mindsets of the characters depicted in the novel based upon both the Southern setting and the fact that both take place during a point in history where racism was at a high.
Another example of the impact which the setting has on the plot is the reliability of of the narrator. If one were to come from the North and the actions in the text are not something the Northerner can see happening in the North, the reader will find the narrator unreliable. What is happening in the text cannot be justified based upon the fact that the actions are not believable.
One last example regarding the impact of the setting on a plot is texts which depict the future. Many times, the futuristic setting allows a reader to engage based upon the fact that the setting has not happened yet. This allows the reader to create an image of where and when the text takes place. For example, the setting of The Hunger Games takes place in the land where America used to be. The time is unknown--but, happens in the future. Therefore, the setting impacts the plot of the story in such a way that allows readers to imagine the time and what the land looks like. It gives the reader some freedom when engaging with the text.