My favorite preference in Slack is being able to have the return key send a message. Otherwise I send messages by mistake, sometimes when hitting the Return key by mistake, and sometimes when making a multi-line message and forgetting to hit Option-Return.

When the "don't send using Return key" option is on, hitting Option-Return will send the message, and hitting Return will add a new line.

I am so used to this that I have muscle memory around it, so not having it in Hive is a little painful.