Trope: The Watson / Audience Surrogate #2*
(*I was going to make this a three-part series, but I think Point of View has been discussed to death on writing blogs. Two parts it is! Don't forget to pop in next week!)
Description: The Watson serves as the voice of the audience, asking clarifying questions so everyone understands what's going on. Note that the Watson does not merely state the exposition, nor does he/she necessarily have to be the POV character. There are no limits as to who or what the Watson can or cannot be - they can be male or female, have any sort of occupation (or lack thereof), be brilliant minds or just smart enough to ask the obvious, and so on.
Examples: Dr. Watson from the Sherlock Holmes stories (obviously), Hermione in Harry Potter, Ariadne in Inception
Pros: If the audience is lost or confused, they're probably not going to think highly of the work in question. As writers, we're already at a disadvantage since we only have our words to convey what's going on and can't rely on visual cues. While you're never going to please everyone, we should at least try to keep the audience satisfied whenever we can.
Cons: At the same time, we don't want to treat the audience like complete idiots. And you know how writers are often told to "show, don't tell"? Yeah. Watsons kind of fall into the "tell" category. Care should be taken to not delve into a whole bunch of detailed exposition that may or may not be relevant.
Would/Did I Use It?: Tirani from The Edge of the Sphere probably counts. She helps fill in some of the "rules" of the fantasy universe when the narrative first switches to Liora's point of view. She also serves as the voice of the audience when, later on, she all but asks Liora, "Are you f'ing stupid? What's wrong with you?"