I thought it might actually be fun to do the companion app. It's not. It's simply tedious. Thankfully, the stuff in those chests is also lame and completely unnecessary. In the end the chests are simply a nuisance.
There were other interesting moments like this in gaming history, like when Secret of Monkey Island changed the way people think by removing death and game-overs, or when FPS's transitioned away from quicksave/quickload to checkpoint systems.
The watch makes sense when you consider the phones are getting huge. All the constant checking for incoming messages, the time, schedules, etc, will be awkward on a giant phone, so all that will be pushed over to the watch.
Now, why are they making the phones huge in the first place? Uhm, to sell watches?