What's the Value of a Precedence Diagram?
A precedence diagram is a terrific tool that helps me understand my project, make sure I have
all the activities identified, and understand how they all relate to each other and to the external
dependencies. As I'm going through the process, I always find additional activities that I had
missed, and I go back and add them to the WBS. By working through the dependencies, it
becomes clear what needs to be done first and what can be done later.
A precedence diagram is essential so that I can see how long it's really going to take to finish this project. The critical path is the key element here. That defines the longest path. If any of those activities miss their targets, the schedule starts slipping. I have to have that data to create my schedules and understand which activities have the highest priority. Otherwise, I'm just guessing.
Why Check the Schedule So Thoroughly?
When the schedule is approved by the stakeholders, it becomes one of the project's constraints, along with cost and scope. That means that it has to be as accurate as possible. If the schedule is incorrect but the scope is correct, I'm going to miss the dates, and the customer will not be happy. In most cases, the project will also go over budget at the same time.
A great precedence diagram doesn't guarantee a great schedule. I find that I need to carefully recheck the assumptions that went into the precedence and the schedule after I create them. I ask myself, Is this schedule based on reality? Can we really do it?