Very low bandwidth or resource usage would be some advantages, less so since they made in this java heh.

Email is message exchange with a person or group of people. They can reply at any time.

IRC is a chatroom. You go to it when you want to chat. A lot of software have support channels. You probably don't know most of these people. Unless you are saving them somehow, you don't have a history of the chat room.

I've never used Matrix but it's a instant messaging protocol that allows voice and video.