“Hey Siri, we lost Spot the dog, do you know where he is?”
Siri:”Spot is located 87 feet forward and down 2 feet from the height of the iPhone. Please hold up your phone and follow the Balloon to Spot’s location”
It’s all about spatial awareness.
The “U” in the U1 chip relates to the Ultra-Wide Band Radio Technology (UWB)  technology it uses. UWB can be used for many application and use cases. One use case that will become very large for Apple as they move to AR/MR technology and Apple Glasses is to be able to track spacial relationships of objects. One way to do this is using lasers and IR systems, and Apple is already doing this to some degree with FaceID and Animoji. The other way to do this is via the radio spectrum.
Lots of detail here on a chip that is an important addition to Apple’s custom chip arsenal.