This what most cryptocurrencies shill. It’s the basis for Ethereum’s smart contracts. In reality what this is really useful for is permanently distributing malware preserved in databases stored on every machine that wants to participate. It’s such an amazing attack vector. Since you genuinely can’t change history without disenfranchising large portions of your user base and killing trust, you can just throw all sorts of crazy attacks everywhere. If someone doesn’t put code directly into the insert-and-read-only database everyone has to replicate, you can hijack what the database refers to pretty easily using attacks that have been around since the beginning of trying to break the web.

If that’s not what you were going for, can you give an example where it can actually be used?