The Art of Project Management

2.1. Schedules have three purposes

All schedules, whether for planning a weekend party or for updating an intranet site, serve three primary purposes. The first, and the most well known, is to make commitments about when things will be done. The schedule provides a form of contract between every person on a team or in an organization, confirming what each person is going to deliver over the next week, month, or year. Generally, when people think about project schedules, it's this first purpose that they're thinking about. Schedules are often focused externally, outside the project team rather than within, because they are used to help close a deal or comply with a customer's timeline. Often, the customer is explicitly paying for the timeline as well as for the service provided (think UPS or FedEx). In order to allow customers or partners to make plans based on a given project, a time has to be agreed upon for when specific things will happen.

The second purpose of a schedule is to encourage everyone who's contributing to a project to see her efforts as part of a whole, and invest in making her pieces work with the others. Until there is a draft schedule suggesting specific dates and times for when things have to be ready, it's unlikely that connections and dependencies across people or teams will be scrutinized. Instead, everyone will work on her own task, and tend not to think about how her work will impact others.

It's only when the details are written down, with people's names ...