Streams are opt-in. Topics are transient and fast to create, and everyone in the stream will automatically see the new topic. You also get per-topic read positi

Streams are opt-in. Topics are transient and fast to create, and everyone in the stream will automatically see the new topic. You also get per-topic read position tracking, and stream members can mute individual topics if they want. You can also view the entire stream at once (or even all streams!) with the topics interleaved. The sidebar shows the most recent topics in each stream, so inactive topics are eventually hidden from the main UI (though you can still dig them up if you go looking for them).