A killer use of Discord... push-to-talk audio connection to everyone else in the room.
If your team is on-call and incident management could be improved, just try putting your team in a Discord room and see what happens. Don't put managers in there, just the engineers.
I'd hardly call it a killer feature when it's something Teamspeak, etc have had for ages.
The killer feature, i.e that which sets it apart from the rest, is the rich text chat and that it's free.
I thought the killer feature is that it is free and convenient. No one has to do any work to setup a server like with Teamspeak or Ventrilo. It has been a long time since I played video games, but back then those were the two popular options.
If your team is on-call and incident management could be improved, just try putting your team in a Discord room and see what happens. Don't put managers in there, just the engineers.
It works great.