[brianogilvie]

In strict GTD, actions should only have due dates if they really have due dates. If I have to get my taxes filed by April 15, I had better give that project a due date of April 15. But if I just think it would be nice to have my garage clean by April 30, I should not give it a due date, because there are no consequences of missing the deadline.

One of the basic principles of GTD is that you should not impose artificial constraints, like fake due dates or numerical priorities, on your projects or actions. The reason is that you can't really fool yourself, and giving projects artificial deadlines dilutes the impact of real deadlines. It's like setting your watch 5 minutes ahead so you won't be late: once you get used to that, you have to set it 10 minutes ahead, and so forth.

Instead, you should cultivate the habit of reviewing your projects/actions frequently and working on what can be done in the contexts you're in, with the time and energy available to you and your immediate sense of what is important to do.

Context lists and focus are one way that OmniFocus attempts to implement this. Flags give you another, binary way of indicating what you think you should be doing.

A Due Date perspective should be used only to act on things that really are due soon--and that seem more important than other things you could be doing. I have one that I review every day to make sure nothing's going to blow up in my face. But I tend to work in Context mode with my actions grouped by context and then sorted by due date. That way I can see, in each context, whether I have anything coming due soon that needs attention, but I can scan the entire context list and see whether there's anything else that doesn't have a hard due date but that is important enough to work on now.