There are several reasons why you might need to unpair your Apple Watch from an old iPhone, most of which are pretty obvious. Whether you're selling your Apple Watch or trading it in, you'll want to make sure your sensitive health data is removed from the device. Furthermore, unpairing it ensures that the next owner can use that watch with their own iPhone.
Unpairing your old Apple Watch is also an important step if you’ve just bought a new iPhone. While Apple’s iCloud setup in principle enables you to switch your Apple Watch from your old phone to your new one, you do sometimes need to unpair the device from your old iPhone before pairing it with a new one.
