Theres several options actually...
An admin can set the profile to be viewable by guests, which includes web spiders; so you COULD end up with a "private" email shown to the public...
so, it can be used as:
1. A spam deterrent whereby users can insert their email such as: gizmo[at]undergroundnews[dot]com
2. As Rose points out, you can use it to allow some people to spam you with seemingly board related material to another email address.
