The way that you're encouraged to architect your code makes it really easy to separate a specific piece(s) if you need to. The functional, no-side-effects approach combined with Elixir's ability to easily communicate between nodes means that if I need to separate a particular set of functionality to certain servers...it's just moving things around.
If I take a function call_me(arg1, arg2) and it returns a result without side effects, it's no different for me to say call_me(node, arg1, arg2) because it's still going to give me the same result just from a different server.
This flexibility means that I can comfortably built a monolith and not have to worry about having to untangle it later if I need to. I love it. It gives me long term peace of mind with short term productivity.