I am grateful for the delete key (backspace, undo). Although you cannot always take back your words once they have been said, the written word gives you an opportunity to think about what you are going to say before you make it relatively permanent. I know that "the Internet is forever," however, sometimes by writing out our thoughts we have a better opportunity to see them. And sometimes we can catch our thoughts before they become hurtful or shameful to others.
Perhaps that is why I prefer writing an email, or even a real letter, to calling someone. It gives me a better opportunity to think about what I want to say and time to word it so that my meaning might be better understood.