There are two things. First, although the above transformation is theoretically possible to achieve with statically typed language, it is for sure harder in practice. In contrast, in Erlang it is super easy and natural although it may often seem as ad-hoc. But being able to do something like like on the fly is tremendously useful in practice.

Second, which is more important -- in my first example, I forgot to mention about the ability to use two versions of the same module at the same time. Check the thread below for more details.