A huge benefit to Discord specifically is that it is multi-platform - you can be chatting on a computer, and then pick up right where you left off on your mobile device with a customized app, that is significantly easier to use than a web-based mobile-site forum chat add-on. It is also a lot better for sharing pictures, smooth private message system, etc. Lots of benefits really.
At first, I was a little 'meh' on discord, but once I really started using it, I think it's probably one of the best chat systems I've used.