Comment 2 for bug 550502

I believe it basically means it drops the privileges you authenticated for. IE you probably got a password prompt recently that asked for your password to allow you to do things you might not want every user doing such as installing packages, adding/deleting users, changing time, partitioning the system, ect., when you entered your password and told them you really are user who has permission to ask to do that you gained ability to use those system privileges for now. When you drop all elevated privileges, you loose the ability to change those things unless you put in your password again.