.ex files compile down to beam files, which can be executed later, while .exs is compiled into memory and executed on the fly.
.ex has better runtime performance and it’s easier to include and load other files.
When I’m writing Elixir library or application my source code is written in .ex files.
I use .exs for commands, scripts, config files, test or anything else that is short lived. These files don’t have be precompiled and you can just run elixir on them.
