The obvious benefits of a Gantt chart and their utility as a project management tool to map out who is doing what and when will they be doing it have already been explained quite will in the posts above. One thing that I wanted to add was the usefullness of the Gantt Chart to the project team members, not only the project manager. I reference the Gantt Chart for the project that I work on quite almost daily in order to ensure that I will be meeting all of my deadlines on time. It also allows me to see when other parts of the project will be completed. Whenever we hit an unexpected delay, we try to incorporate it into a revised chart in order to keep it realistic and up to date.