Personally I find it hard to follow conversations in Discord, seems to be a big monolithic list of messages. However, I’m also struggling with this forum as there doesn’t appear to be a visual indication of what topics/posts you read. Also no Private Messages or, as mentioned elsewhere, the ability to attach pictures or other files. Highly useful features IMHO.
I help run a couple of SMF based forums but these require server/hosting facilities. I like Discord because at the entry level it’s free and hosted in the cloud. Not mentioned above but you can also share your screen or just a Window. Often useful when demonstrating something or helping another out.