Erlang and Elixir are excellent glue languages, and excellent in handling a lot of network requests at once. You’ll be very hard-pressed to find another runtime that does these things so rock-solid and fast.
That being said, they definitely fall short if you need mega-fast processing that requires pure CPU muscle – like various matrix calculations, deep learning, image processing, those kinds of things.
People praise Rustler because, as @NobbZ said, it makes it very easy to integrate your own Rust code with your Elixir code. But that’s only if you need it. Most of the BEAM projects are perfectly fine being Erlang or Elixir only.
