Students are the active users of the technology. They construct what is said, and actively synthesize the course material. PowerPoint is teacher-centered. It puts the instructor at the center of the action, promoting passivity on the part of students. Whether students are attending or not is incidental to using PowerPoint.
Students decide when and where they interact with the course material and each other.
This allows them to work when they work best, and have the most time to devote to their work. Students are also in control of how much time they spend using it, and when they make their communication public. This is particularly important with electronic conferencing, in that more reflective, introverted students can take as much time as they need to compose what they want to say, and then post it when they are comfortable with what they have said. Since conversation is no longer in real time, the quick and assertive no longer dominate. This levels the playing field for individuals whose voices may not be heard in the traditional classroom discussion.