I just read dozens of comments that in effect say "This can't be any good because I, personally, cannot think of anything it might do."
Try this:
1. You are at the grocery store heading for checkout, and as usual, did not make a shopping list, so you ask Siri "did I forget anything?" Siri has seen your pantry and fridge and saw what you placed in the cart. So it can say "There are only three bananas left at home and not much coffee either. You never told it anything it just passively watched.”
2. You are in China and know only about a dozen Chinese words and can't read it at all. But you would like to walk to a place you heard about for lunch. The Siri-pendant can read the street signs and tell you how to get there. Or maybe it will tell you which bus to take because it can read the LED sign on the front of the bus and tell you "not this bus."
3. You are a salesperson and deal with hundreds of potential customers. Siri-pendant sees a person at a distance and tells you, “That’s Bob, you last saw him 18 months ago in San Diego at that conference, ask him about the server room installation.” No need to ask, Siri-pendant just noticed that Bob saw you and is headed this way. She knows how forgetful you are with things like this because she has been with you for a few years.
4. You are leaving to go out and Siri-pendant sees you are near the door and says "I think you forgot your wallet, it is still upstairs."
Obviously, this is not today's Siri. Apple has already said they are working with others to give Siri's voice a better brain.