Thieves love to steal iPhones because they can quickly sell them for easy cash.
The first thing a clever one will do is swipe down and turn on airplane mode
Find My and that will scare away some thieves from trying to run off with the phone
Scared of being caught may simply ditch the phone and then you may be able to recover it using the Find My app.
Note that if you change this setting and try to test it, make sure you're not looking straight at the phone or Face ID
Have them try to swipe down and access the Control Center.