Email is so widely used that most people have several email address just to keep the madness to a minimum. For example, it's normal to have a work email, personal email, and a "junk" email that you give out when doing so will most likely result in unwanted spam and solicitations.
And, with all this email flying around, how many emails do you actually open and read? How many do you just delete? These are important questions, especially if you regularly send out email for your business.