Having a personal email on your domain is a really smart way to make use of your web space! Your email address reveals your unique online identity to your messages recipients. Instead of having a meaningless ID on your yahoo mail like email@example.com, you may have an easily memorable address like firstname.lastname@example.org, email@example.com, or anything that shows who you really are to the email recipient.
Having a personal email is really essential for people who do business! It looks much more professional to send messages via your personal email (on your company's domain) when communicating with your business partners, sponsors, and clients.
Having a personal email is also a convenience. Unlike the Google and Yahoo emails, you will be able to reach your personal email both via webmail access and via convenient mail clients like Outlook express, MS Outlook, Mozilla Thunderbird, etc. Also, the email address you have on your domain name will not show any ads which lower the speed of your Internet connection and lose your time.