For those not on it and for lurkers, I'd like to balance the Discord server's hype here with my anti-community experiences which led me to leave. Everyone else loves it though so I am an outlier.
1. The text channel, ironically called splatoonchat, is hugely off topic, 80% off topic from what I saw. When I wanted to discuss maps, weapons, strategies, etc. I felt it was too awkward to even bring it up and interrupt the off topic conversation, and the rare times I did, no one was really responsive or 'into' it; there was no audience for it. Timezones also make it difficult to follow the off topic anyway.
2. There are secret text channels which you cannot see. From my limited time there, I believe there is a NSTC (Squidboards tournament team) channel and an Azure channel but little is known about them other than a confirmation of the former by SM. I don't like the sense of 'everyone is somewhere else and unavailable to the rest of us'.
3. There were never enough S ranks to play a quad with me in Squad Battle. And no one was really down to either, I felt like I had to beg.
However, Discord shines in gafhouse and I'll temporarily return to the server whenever it's on. Everyone is brought together and talking in one place.