Comment by truly

The main issue with Discord/Slack is that it is difficult to get up to speed with the context of the discussion. You essentially have to read the entire history, and you might or might not be interested in every topic.

Email is much better, since only a select set of persons receive email on a given topic, making it more likely they are interested in it.

For documentation purposes, Discord and Slack are essentially completely useless, due to poor structuring of the conversations and poor search functionality. Anything with more structure would work much better.

The only case it works well is on small teams that are 100% into solving a particular problem together, and they can context switch every few minutes into the chat.