I’ve changed the default on the summary emails from ‘daily’ (the default) to ‘every two weeks’, because daily was freaking annoying. I think this only affects new users, so existing ones will have to update the setting themselves.
You can change your digest setting by clicking on your avatar, selecting Preferences -> Emails, and then choosing your desired email frequency (‘never’ is an option).
The emails only get sent if you haven’t visited the site for the specified length of time. So if you set it for two weeks and you’re gone for over two weeks, it’ll send you an email summary of popular topics you may have missed.