TL;DR While using Summon via the app, pressing any button on the key fob will stop the car faster due to less latency.
The Summon feature that comes with AutoPilot equipped Tesla’s is pretty great when you need to park in a tight stop. It allows the car to park itself in garage, and to move it forward and backward while standing outside it. In the US they can do this with the buttons on the car key fob. However, outside the US we are limited to the iOS and Android app.
Unfortunately there is a lot more latency when using the phone. The information has go to from your phone, over the internett and back to the car – taking more time than the connection between the car and the key fob. This means that when you have poor reception, by the time you signal the car to stop, it could still roll several more feet before it comes to a stop. The car does use parking sensors to avoid hitting anything, but that isn’t exactly a guarantee.
Using the key FOB as an emergency break
When using Summon via the app, the key fob can be used as an emergency brake. Simply hit any button on the key fob while using summon and the car will immediately come to a full stop. This is a great backup-plan in case you are in a parking garage with bad reception, or there is something in the cars path that it might not be able to detect.