<p>Topics are like email subject lines. The big difference, though, is that they're really short and lightweight. Two or three words will do it. Don't overthink 'em—you can always edit the message later!</p>
<p>Why bother with topics? Well, two reasons: it makes conversations clearer (imagine if email didn't have them!), and it lets you more efficiently catch up on what's happened while you're away—read the topics that are relevant to you, and ignore the ones that aren't!</p>