If you forgot to return a value, a function shouldn't have compiled. In Nim you can easily forget to return something or have a hole in your branching and get a defaulted value, instead of a compiler error.

In some cases an implicitly declared variable feels neat and convenient, but I'm not sure it's worth it.

Ha, I'm quite used to Rust's last-expression-is-the-value and I also get why some would think it's weird but I find it actually works quite well in practice. Each language has its gymnastics and special moves, I guess. Back to Pascal, I'm not opposed to Result usage per se and I understand the appeal since it's what I grew on. My concerns are more about code maintenance in long-ish functions - I don't have a particular example of mis-usage, but I'd be wary of late reassignments overriding a previously set value. Separating exit points from return value assignment could let code become hard to follow and create situations where it's easy to misread the actual outcome.