A favorites list will allow you to create (up to 4 lists) a list that you add channels too. So in this way you have to "opt in" every channel that you want included in the list.
But if there are channels which you don't want to appear on any list (all, all sub, all HD, etc..) Then you can "lock" them out. When a channel is locked out, it won't appear in the guide. This is good for Adult channels which often have racy program descriptions.