And then? You can not turn it on again, without also activating the beacon.

I wonder if stolen iphones have any value except for hardware parts.

While walking and without alerting the person you just bumped into to the fact that you just took their phone? More realistically, a well-prepared/tech-savvy thief could just drop the phone into a Faraday bag in their backpack/pocket, or alternatively just turn off the phone!

Fortunately, the one that my friend encountered didn't do any of that.