The major difference is that offchain we use contracts verified (and written to be verified) by humans. For a fridge that might mean that you need to send photo

The major difference is that offchain we use contracts verified (and written to be verified) by humans. For a fridge that might mean that you need to send photo evidence and have a mechanic look at the fridge. In case of disagreement a human court will decide the outcome. It's not always going to get it right, but it's a lot harder to scam systematically. For smart contracts to bring the value of machine verified contracts without human intervention we need the data provided to the system to be verified. Without verification that all parties agree on we will always need human intervention in case of a dispute.