Show my email address

Hi,
can you please explain me what "Show my email address" check-box is for? The field on user_profile_form has description "Use my private email address as a sender for notification mails to users I have sent private messages to. If unchecked, the notification will be sent by a generic account." and it's unchecked by default.

It's not clear to me what it does. Can you explain me what is it for?