It&#x27;s related to a productivity strategy called &quot;inbox zero&quot; where you immediately deal with every email in your inbox when you check your mail.  &quot;Deal with&quot; might be to delete it if it&#x27;s junk, respond immediately if you can, or defer it to later.  A lot of these clients are aimed at making this process as fast and efficient as possible.  So taking actions on an email are often just a swipe, and there are facilities to defer an email to a particular time, or adding it to a to-do list.<p>It&#x27;s mainly intended at people who get too much email.