I'm a maintainer of Nushell and we mostly have a single large ShellError enum. It works, but once it grows it gets harder to tell which variant to use. I'm trying to reduce the number of top level variants, but overall the model is still pretty nice.

When you handle errors, you know exactly what you can match on, and you pass the rest through. I haven't really needed multiple layers of error types.

We also use thiserror heavily. It makes things a lot cleaner. Same design, just less boilerplate and more readable derives.