If the user wants to send a copy of the email to a certain set of users then such users can be added to CC List. Such users will get a copy of the email.

Points to be noted:
The users to who campaign has been sent won't be able to see the users who are added to the CC list.
The users who are added to the CC list needs to be part of the audience/contact master.
The CC Email ID will receive only one copy of the campaign, not a copy against every end user.