It's a chatroom with different channels for different purposes. The benefit in my opinion is that you can easily have a back and forth conversation in real time which is not something you can achieve on reddit. It's not solely about juggling either. Infact, you can discuss literally anything in the off-topic or general channel and compared to reddit you can post stuff that is rather low effort.

You will usually get more interaction on the discord than on reddit aswell. I see reddit and discord as two completely different things. Reddit is for high effort posts that you want to share to the juggling community and discord is for interacting with other jugglers.