Let's look at an example of communicating the old way, using the different roles from MSF for Agile Software Development. Obviously not all teams will do things exactly as described, but the roles as described are valid enough to prove the point.
Let's imagine project development the old way: The business analyst defines the project vision and requirements using Microsoft Word; then he passes this document off to the project manager. The project manager begins to create a Microsoft Project plan, breaking the requirements into tasks for the developers to execute. While doing this, the business analyst discovers two more requirements. Instead of updating his Word document, he just e-mails the new requirements to the project manager included in his project plan. Of course, the e-mail server is offline at that time, so the project manager never receives it.
Meanwhile, the project manager has printed out the project plan for each developer, and given each a copy, showing them the work they are to do. The next day, however, one of the developers leaves the company. The project manager goes back to his project plan, and begins to readjust everyone's schedule. With the schedule readjusted, he e-mails the new project plan to everyone, with their new duties.
However, one of the developers, whose duties have changed in the new project plan, doesn't check his e-mail. Instead, he continues to work from the original plan that was printed out, and begins to ...