Every project has at least one milestone - the end. If that end is more than a week away, establishing some clear intermediate milestones will improve your chances of reaching it on time.
Engineers are busy people who have many demands on their time.
Some of these demands will be more urgent than the far-off end of your project. Other demands will seem like much more fun. A good set of milestones will give engineers a clearer sense of direction, help them to prioritize their time, and enable them to measure their progress. Unfortunately, many project leaders don't successfully establish clear milestones, resulting in projects that gradually drift off schedule. Use the right number of milestones.