TL;DR… Find My got a co-worker her stolen phone back
Shortly after Apple introduced “Lost Mode” in iOS, a coworker had her iPhone stolen by someone else who worked in the area. Her Lock Screen photo was her and her son, so it was immediately evident who this phone belonged to and would have been easy to return. She left it in the restroom, realized it almost immediately, and went back get it. Gone. I remembered Lost Mode from the keynote that year, told her about it, and asked if she had updated to the latest iOS. So she signed into Find My from a desktop PC and she enabled it. The phone didn’t show up immediately because the dude who stole it did think to immediately power it off, but later that night he turned it on from his house. She got a notification, a map location, and an approximate address from which the thief was able to be identified. He confessed when confronted by HR and returned the phone.