Sometimes a message contains information about some action that you need to take. For example, in the picture, the message from Ben Smith in Mark Lee's Inbox reminds Mark that he needs to promote a line of office furniture that his company recently introduced.
Mark can drag the message from his Inbox to the Tasks button in the Navigation Pane to quickly start a new task. He can change the subject to something more task-like, for example Show office furniture to Coho, and then save the task. The task is added to Mark's task list.