Q. What is the difference between a participant and a follower? Are they the same thing?
A. Participants have more privileges on the study group, and are the ones that will be actively involved in it. They can post messages to the wall, post comments on the study group tasks, create new tasks, and help improve existing ones. Followers can only see the study group activity stream in their dashboard and in the future will also receive optional notifications by email. As the number of participants in a study group grows the number of comments, wall posts ... that participants and followers have to read grows and can become overwhelming. The follower role is designed for study groups that can not handle big groups of participants and need to restrict how many people is actively involved.
http://qa.p2pu.org/questions/87/what-is-the-difference-between-a-participant-and-a-follower