I'm pretty sure top 10 are contacted through discord, and there are also channels in the discord dedicated to the jam, some of which Acerola uses for jam-specific info (like the channel 'jam highlights' which covers top games and security related things).
This is my community game jam and discord is where my community is, so if you want to interact with other people who made games or see my announcements in regards to the jam/games I liked then yeah the discord is nice to be part of. It's not super necessary though.
