It is highly interactive and dynamic, yet performant. And it is not only about scientific computing, for almost any application can take advantage of interactive, modifiable system, where you can explore your state at any point. In others, more static langs good debuggers help with this to lesser or larger extend, but it is not the same from my experience.

So better question is: in which circumstances would you choose Julia over more mainstream-y alternative like Clojure? And here scientific and numerical angle comes to play.

At the same time I think Julia is failed attempt, with unsolvable problems, but it is a different topic.