What are the best practices to substitute variables in a string

[shanesveller]

If you want peak performance and slightly harder ergonomics, IO lists (aka IO data) are very hard to beat, they’re how Phoenix views are so fast.

https://hexdocs.pm/elixir/v1.10/%20/IO.html

ElixirConf 2019 - High Performance String Processing Scripts in Elixir - Johanna Larsson

Elixir Performance – Using IO Data Lists

Efficiency of IO lists in elixir/erlang

I have read about the efficiency of IO lists. However I am still not able to wrap my head around it. How exactly is nesting of IO list more efficient than concatenating strings ? How exactly is IO list more efficient when there are a lot of repeating words ?