What does the arrival/inclusion of Dill in the story add to the novel (influence on plot events or characters) ?

In Chapter 1 of To Kill a Mockingbird, Scout is reminiscing about Jem's broken arm, an event that happens later in the story. When she considers how the chain of events surrounding his broken arm began, Scout blames the Ewells. However, Jem believes that Dill is the reason it all began. Dill gives them "the idea of making Boo Radley come out."

Dill, otherwise known as Charles Baker Harris, stays with his Aunt Rachel in Maycomb County during the summer. Once Dill "had been studied and found acceptable," he and the Finch children spend a great deal of time together. According to Scout, "The Radley place fascinated Dill." It is in this way that Dill contributes to the plot development. Before Dill, Scout and Jem are aware of the rumors and superstitions regarding Boo Radley, but Dill is the one that dares Jem to touch the house. After Jem completes the dare, Scout recalls seeing a shutter move in the house. Just as the children are interested in Boo, he becomes interested in them as well.