I wanted to do this production of J.B. Priestley's An Inspector Calls in the round since all of the action takes place in a single room. The audience literally makes up the walls of that room, which fits well with Priestley's message of community and taking care of one another. As the characters discuss the horrible things they've done, the audience is literally watching itself watch these events. They are both observers and complicit in the action. Behind the audience risers, we placed a couple of offstage areas for the actors to be when not onstage (Mrs. Birling and Shiela are banished to another room at one point since the discussion is not "suitable" for their hearing; Eric spends a lot of Act II in his room), and by keeping them in the view of some of the audience, we tweaked the experience each audience member had of the play and its characters.
In working with the actors, the small role of Edna the maid was enhanced by allowing the actor to eavesdrop on conversations and interact in subtle ways with the Inspector. Again, some audience members were aware of this and some were not.