When to use BCC and When not to
I've noticed there are at least two good times to use the BCC in an email and otherwise the use can be disingenuous and dangerous.
1. Use BCC when emailing a group where it would be inappropriate to share the distribution list with all the recipients. For this purpose you can often use yourself as the visible recipient so it's clear there is a distribution that you're not showing.
2. Use BCC in a reply after an introductory email or where a party is no longer relevant, noting in the response that you are moving them to BCC to continue the thread without them.
Otherwise, in the case where you want to advise somebody of the content of a email, but you don't want to add them to the thread or advise the other party of the communication, you're better off sending the email/reply without a BCC, and then forwarding the email/reply to the third party. Else, your BCC could be a setup for the BCC'ed third party to reply to the thread if they don't notice the BCC - something that clearly alerts the original recipient to your hidden intent. Also, a forward is somewhat less disingenuous in that you are not hiding the communication, you're taking action after the fact.