Last night a group decided the #1 online annoyance, other than spam and spoofing, is those who use "Reply to All" to email that doesn't request responding back to everyone. The "Reply to All" people seem to use that feature with most email they receive, not just select ones. And those who reply to only the sender, seem to routinely just reply to sender (unless requested otherwise).
"Reply to All" is also a typical way that an email goes to those not realized were blind copied and the responder regrets it. As the saying goes, just because you can, doesn't mean you should.
I often copy and paste a portion of an email to the sender into a new email rather than hitting "Reply" so my email response can entirely leave a thread. Too many group emails are carelessly forwarded to others, along with comments from others only intended for the sender.