The main purpose for collecting each commenter’s email address is so that I know you’re a real person, and to help personalize your experience on the site. If you send me an email, the address that you send it from will never be shared.
If you write personal info like your full name or your email address in the body of your comment (or in the “Name” or “URL” field) this info can be viewed by anyone reading the comment section of that post. Your email address, when entered in the “E-mail” section of the comment form, will remain hidden from view and will not be shared.