The intent is important because it becomes the lid on the project. Without it, it is far harder to stay on track and make meaningful progress in finite time. In a good company everyone involved knows the risks that may make the schedule and budget slip and acts accordingly. Done right, the pressure does not rise unduly shortly before a milestone. It should rise earlier, but also to a much lower level. And a good manager will know when enough is enough and move the deadline before it becomes too stressful.
