An obscure example of this: last week I was in a forest in Asia, far from any civilisation, with my phone in a bag of rice after getting it wet. I started getting texts on my watch and frantically untied the bag to check my phone as I thought it had turned itself back on too soon, but it was dead!I actually didn't know that, thought we could only add a playlist through Apple Music and listen to that via Bluetooth while my phone is away from me. Thanks for the tip.
Took a while to figure out that my friend with a local SIM had turned on his hotspot and the watch had automatically zapped onto it - almost had a good ol' ghost mystery on our hands!