Tasks that must be done by a certain day need a deadline date. Deadline dates are the final day of reckoning. While hard dates ensure that “must do” tasks get started on time, deadlines help you plan and make sure they get finished on time. Deadlines also apply to tasks that expire but don’t really have bad things associated with them, like coupons.
Deadlines need to be considered every time you make scheduling decisions, so this date should be prominent. However, they are never used for sorting your lists! Sorting a list by the dates when you are already in trouble makes no sense. Instead, soft dates and hard dates serve that purpose—they help order your lists by the action dates needed to prevent bad things from happening.
See also smart dates.