What data can possibly reside on your phone to make it worth more than $500 (or whatever a used smartphone could be worth)?
All "data" created on the phone is automatically uploaded to one cloud or the other so it should not be that.
If you're thinking banking details, I really hope that it's not in the clear if someone gets into your phone. All my banking details are secured by external "BankID" with 10-digit passcode, my phone alone gives no access to any valuables (banking, stocks, nothing).
Identity theft? There's nothing on my phone that can't easily be accessed directly via online databases, nobody would go through the trouble of trying to steal my phone to get that data.
Some of us create and can have intellectual property worth millions. Some of us have access to critical systems. Some of us have banking and investment apps with funds many orders of magnitude more than the value of a phone.
The thread I replied to was stating that the security of access wasn't important and that only activation lock so someone can't gain value from the hardware itself was important. That's wrong. It's not a big deal if I lay out ~$1400 for another phone, my data in the wrong hands would be much more painful.