I think we've all done this: you get a differential in your mailbox, review it, add an inline comment, and then go to lunch. The next day your coworker bugs you because you're blocking them, because you never actually pressed submit at the bottom of the page. Phabricator helpfully saves these staged comments (indefinitely?), but it'd be cool if it could warn me by email if I leave one unsubmitted for an hour or two, to limit lost productivity from a common mistake.