In the session video, if the App is in background mode, when isStationary=true, jumping out of await will stop listening to save power.
Suppose the device starts moving again, how does the developer re-listen?
How to re await CLLocationUpdate.liveUpdates in backgroud
The example in the session was just to demonstrate how to stop updates by jumping out of await, and happened to use isStationary as the trigger for that. This is not something you need to do. You should only jump out of await when you no longer want to receive location updates.
Power savings come from the system not running your app all the time when the device is stationary.