If you are an administrator, you can create a member group for each department, committee, or team represented in your site. When you create a group, they can share and edit their own documents, hold their own discussion forums, and email links and event reminders to each other.
Creating member groups allows you to easily set application permissions for the entire group at once. For example, when setting permissions on a folder in the Documents application, you see a list of all the groups in your web office. You could assign Manage access to all members of the "Marketing" group for a folder called "Marketing Plans." Similarly you could use groups to set permissions on discussion forums and host an online discussion for a limited audience.