I have this Conversation for clarity with all my managers.

FieldMeans
TOEither I need you to do something, or I’m replying to something you asked.
CCI need you to know about this, and you may need to step in or do something if I can’t. It can also be that I need the recipient to know I have included you
BCCI need you to know about this, but I don’t expect you to be involved or mention it to others.