I personally would want to use an immutable functional language wherever I can and only not use it if I have a good reason not too. Immutability makes reasoning about programs significantly easier, especially if they rely on concurrency.
And for finance it particular it's a very natural fit because there's just a lot of transformation of data and business logic.
And for finance it particular it's a very natural fit because there's just a lot of transformation of data and business logic.