Deadlines feel like they are mainly useful to induce stress and urgency. The stress and urgency being useful (or important) is another matter.
In a perfect world (for me, from my point of view), there are no deadlines, but rather short plans and enough understanding of the plan to decide whether doing something specific is useful or a hindrance (and to what degree) for executing that plan.
But alas, deadlines are easier to decide on.