I personally think that the most important impact that functional languages make isn't in their direct use (which can be very powerful), but more so in their in

I personally think that the most important impact that functional languages make isn't in their direct use (which can be very powerful), but more so in their influence. Bringing functional features into more main stream languages allows everyone to take advantage of powerful features/patterns. The first one that comes to mind is pattern matching. All your ML derivatives have had it for years, and it's an extremely powerful concept. Unfortunately, most people (myself included) had never heard of it until it hit more main stream languages like Rust and C#. Streams and the more wide spread use of anonymous functions is another great example of functional concepts making imperative languages much more expressive and powerful. I don't like writing in pure functional languages very much, but I do enjoy a lot of the power the have and how we can make these concepts more accessible to traditional imperative languages.