Add Cc and Add Bcc in compose mail

Add Cc stands for Add Carbon Copy
Though the mail can be sent to many IDs using the "To" column by typing multiple entries separated by a comma; Multiple entries in Add Cc column does the same thing and is usually used to convey information for courtesy sake. A carbon copy of the document is sent to them in literal sense.
And again if you are sending to multiple IDs from both To and Add Cc column; all the recipients are capable of viewing who all has received the copy of the mail.
Here comes the role of Add Bcc - Add Blind Carbon Copy
If you do not want your recipients to know whom all the copy of the mail has been dispatched; then adding multiple ID's in this column is helpful.