[Jtsummers]

Addressed in part by dmitriid and dnautics, but:

1. You can use this during development (where the tight feedback loop is very nice).

2. You can use this during deployment (after verifying that the process will work as intended, hopefully).

(1) is something you could do every day if it was your daily driver language. (2) would happen less frequently (well, as frequently as you deploy) but permit you to do partial updates without bringing the whole system down.

It's worth remembering that deploying Erlang (and Elixir) can be more like deploying with microservices or applications to an application server. You don't want to bring the whole thing down just to change out one part of the system, so you can update just the parts that have changed and need to be updated.