Hey @asibbald! Which part of this explanation felt unclear to you? The intended take-away here is: By using the PG2 adapter, your code will work even if you deploy your application in a distributed manner". This is what we mean by:

clients across distributed nodes of our app can subscribe to a shared topic and broadcast to that shared topic, because PubSub can directly exchange notifications between servers when configured to use the Phoenix.PubSub.PG2 adapter

It’s not important to understand the mechanics of the PG2 adapter or Distributed Erlang beyond that, and I don’t feel that a lack of that deeper understanding will prevent the reader from building out the feature in this section.