Or rather, it isn't useful in production in any way Python is not, and there's little reason to choose a weird stunted Lisp that offers few advantages over its host, an established language with a huge community.
Syntax transformation via macros can be a significant advantage when the semantics of the language don't support an abstraction that's shaped like your problem.
I can see even in larger python codebases some places where e.g. support for some s-exp minilanguage could be useful and implemented rather trivially via Hy, or also to embed some processing kernel which is well suited to being written in lispy semantics (e.g. symbolic programming, etc). Another use could be to define core primitives in python and glue them together using a heirarchy of configuration+Hy macros to generate specialized '__main__' programs for task-specific use cases.
