The futuristic setting of a tyrannical state is important to the plot of Fahrenheit 451.
Setting is the specific time and place, customs and traditions of the people, and the mood.
The setting is sometime in the future, where books have been outlawed. It is not too long after now, because some people still have books illegally. Houses are fireproof, and instead of putting out fires, firemen burn books.
The conversation between Montag and Clarisse in Part I demonstrates the effect of the setting on people.
"Since I was twenty, ten years ago."
"Do you ever read any of the books you bum?"
He laughed. "That's against the law!"
"Oh. Of course." (Part I)
Clarisse comments on how people can arrested just for slowing down, sitting on their porch, and doing anything besides drive fast and watch television. Bradbury is establishing the domination television has over people’s lives, and how empty and unhappy Montag is.
This setting causes us to question our own lives, and the role of books and tv. The importance of books to making us human, and the soul-sucking functions of passive tv, are some of Bradbury's main themes. Books are a symbol of our humanity, and without them we are nothing.
In part, Bradbury wrote in response to other totalitarian regimes like the Nazis, who selected books for burning as a way of controlling the populace.