All recipients can see all other recipients in the TO and CC fields. However, nobody can see the names or address information for people included in the BCC field.

In business terms, I might send a message to Joe with tasks or action items for Joe to do. I might CC some people so that they are aware of what is going on, but so they understand the action items and tasks are not for them- they were just copied, not direct recipients.

The BCC field sends a blind copy. You might use that if you wanted to send an email to Joe but you think Joe is a slacker- so you BCC his superior so that they know you asked Joe as well. Then you can see if Joe will do his job and his superior will know as well. That is just one example of a "legitimate" use of BCC.

In reality it makes some sense to BCC everyone to maintain the privacy of all parties.