The problem is not "importance" of the message per se, but the "immediacy" of the contact. People seem to feel that they have to send a message, or reply to one, RIGHT NOW NO MATTER WHAT.
It's nuts. I've felt the "pull" of the immediacy myself at times -- it's hard to ignore. I quit smoking many years ago, and that was actually easier in some respects.
i pull over. always, no exceptions.