LPT: When sending professional emails, the To: field is for the recipients who need to do something or respond to the email. The Cc: field is for recipients who should be aware of the exchange.

If you have a bunch of recipients in the To: field, it may not be clear who should be the one acting/responding.

If you address the email to Bob, but Cc: his supervisor, Bob knows he needs to act and the supervisor is aware of the exchange.