E.g.: you set your inbox to show only unread messages. Then, you take a look at another folder, e.g., the Spam folder, and return to your inbox only to find that the view has reverted back to showing all mail, not just unread mail as you wanted. Hence, the suggestion to make the view setting "sticky", i.e., does not revert back without the user changing it. The "stickiness" should work across login sessions also.