....and that is the LAST place a person wants to leave their email wide open to the next person who comes along!
As a volunteer in a Family History Centre, we see it all the time. Somebody goes to Yahoo, and there's a stranger's email for all to see. When signing in, it's too easy to miss seeing that box is already pre-checked - I know this problem and have still missed it myself! If you offer the unchecked box every time, the user who does get tired of signing in each time on their own computer can make the choice t check it. As it is now, it appears that Yahoo cares more about promoting their own site than about the security of their email users.