#nostr posts are tamper proof. But the time ordering is not. Let's say I have a signed spend function, I could do two posts at the same time, and the relay would not have a way to know which was first. Using an on chain commitment you can get finality by using an on-chain tx. This allows you to have a tamper proof SERIES of events, such as a ledger or contracting system

It's a world computer on steriods!