I'm also mostly in favor of static typing, but I think the major usecase of dynamic typing is having a broad sort of polymorphism, where you're free to think of variables just as what they can or can't do, even if they're immutable. Of course that behavior can still be implemented with statically typed languages with interfaces/traits but it's more work. It's worth noting that it is also much safer, and it helps you iron out your model's inconsistencies, where dynamic typing often hides that you're doing something that fundamentally shouldn't make sense.