Also, if there is actually an invalid state for the result type, and your type system has a sum type here, it can implement the sum type by overlaying it, producing machine code that's just as nice as for old school C or C++ programs yet programs that have readable sum types. The actual best of both worlds.

Rust for example promises that Option<NonZeroU32> is the same size (four bytes) as u32, even though it has much more appropriate semantics for some cases. I can't accidentally end up with a zero where I wanted anything else, and I can't easily forget to handle the None case where there wasn't a non-zero answer.