I guess the upside is that you end up with a "compiler" that checks the invariants of your project and that domain rather than strict type safety. I love static typing, but I did try Elixir w/ Phoenix recently and was impressed that they were able to implement compile time checks like verifying that all redirects are valid routes, etc. Depending on what you're building, having a few small domain specific checks like that could be more valuable than strict type safety.