NOTE: In newer versions you can defer both due date and threshold date and this discussion is moot.
The deferring functionality in Simpletask is the MYN defer to do/review deferring.
It does not intend to be a due date. It is just meant to get low priority tasks out of the way for now and have them reappear at a certain time in the future (1 week, 2 weeks or 1 month). To achieve this I filter task with threshold date in future. When the deferred start date arrives, the tasks will automatically come back into active view (with the right sorts)
You could also use this with a more GTD style tasklist. It's a quick way to get a next action out of the way, without moving it to Someday/Maybe. If you skip reviewing future tasks in your daily or weekly review you will not have to review tasks you'll know you will not do any time soon.
So why not use due:date for this? There are several reasons:
- Due dates are generally in the future so it is not very usable for the MYN/1MTD concept of date in future -> out of view.
- Defer-able due dates lead to undone and often postponed tasks. A task should only have a due date if it absolutely needs to be done before that day or something bad happens. It should not be a "I wish it to be done on that date" indicator. Both GTD and MYN agree this doesn't work.