Cool - glad you brought up the smart lock example. How does that work without trusting (presumably off-chain) software/firmware to honor the change as to who should be able to open the lock? The smart contract might be iron-clad in showing who should have access, but at some point, that has to be interpreted and executed by a real-world entity, human or machine.
In other words, standard contracts work just fine (without any lawyers involved) when everything goes to plan. It's the failure cases that matter, and it's not hard to imagine a compromised lock (or an entire company's locks if they're connected to the internet for access to the blockchain) that no longer respect the smart contract. So you're back to calling your lawyer to help sort out the mess.