One case where I find it useful, tho it operates in a more limited way, is code in block blocks within code comments in Rust, which are also printed out in the generated documentation. They essentially get ran as part of your unit tests. This is great for making sure that, eg, your examples left in code comments actually work, especially if they’re written in a way that functions like a unit test.
The version that’s stuck in my head is Japanese so this is a translation.