In chapter 1, the Radley place is depicted exactly as what you imagine all scary, creepy haunted houses to be like. "Rain-rotted shingles drooped...oak trees kept the sun away...the remains of a picket drunkenly kept guard." These descriptions are very dark and serve the purpose of setting the mysterious mood, the slightly dangerous air, the unsafe and perilous atmosphere that is to surround the Radley place and its enigmatic inhabitant, Boo. It is a great ghost or monster-story set-up: a creepy house, "a malevolent phantom" that peeped in people's windows at night, the gossipy threads that existed about Arthur and his abuse of the family. All of this aids in creating an atmosphere of suspense that much of the first chapters revolve around. The audience, with the children, are to feel fear and trepidation whenever the Radley place is part of the story.
In the end, the Radley place and Boo himself might symbolize a running theme throughout the book, which is that things are not always as they seem. You shouldn't judge a book by its cover; you need to discard preconceived notions about people and see them for who they really are, good and bad. This applies to the entire story of Tom Robinson and Mayella, to Boo Radley, to Mrs. Dubose, and is a major point of the novel. The Radley place is one of the most important symbols of appearances being deceiving, considering what Boo does for the children at the end.