I can finally have a single platform for communication. Voice chat, text chat, group chats, friends list, async communication, unlimited logs (no 10k max msg nonsense), webhooks/integrations that let me do far more than IRC bots ever did. All of it under one account. Oh and the client doesn't suck, unlike Slack's. It's fast. The voice quality is superb.
As far as productivity goes, I get far more done with it than I ever did with IRC. The addition of being able to hop on voice very quickly is insanely good. Screensharing and video chat coming this year as well, I'm pretty excited.
It's to the point that I bought Discord Nitro (their premium offering) the day it was released, for no other reason than to give them money.
I hope the question of protocol openness gets resolved; until then, IRC just doesn't cut it for me anymore. IRCCloud.com helps, but their interface is super slow with lots of channels and IRC itself simply has no support for the thousands of improvements that have been made in communications the past 30-something years.