We made heavy use of Primastic's schema when we felt we needed guarantees about the shape of the data, this help in areas where you want the extra checking and documentation.

In practice refactorings such as changing Address->MaybeAddress didn't hurt us so much. With good test coverage also, it's not a huge issue.

Clojure code-bases tend to be more much concise and well organised, so refactoring based on expected data and output doesn't bite as much as people often fear.