When do you put your e-mail addresses in the To: field or the Cc: field? There really are no hard and fast rules — you have to use your discretion based on the circumstances at hand.
As a general guideline, use the To: field if you want to email several contacts while encouraging their response. A response is expected when your e-mail address is in the To: field. ?? Only when your comments are important to the group would you use Reply to All.
The Cc: field is generally used to keep people in the loop (FYI) with no expectation of a reply being required. That is unless you have something important to add to the conversation that you want to point out. In that case, reply to the Sender only and do not hit Reply to All. Let the Sender decide to send your reply to the others involved.
One thing is clear — refrain from playing politics with these fields. Using these fields to make someone feel less important or to make a point by putting them in the Cc: field when it would make sense to include them in the To: field is not right. Doing so is never a successful strategy and can backfire making you look trivial.