The email you use sends a message about you. If all you are doing is personal correspondence between friends then you probably don't have much to worry about.
But, if you are running a business you want to make sure that your email communicates the right message. By using a Gmail, Yahoo, or similar type of address you are reducing the credibility of your business.
In addition, you are likely paying to print that email address on business cards and brochures. You are spending money to advertise another brands name and their is the risk that the address can change or the policies of the company can change.
If you are running a business then it is important that you have an email address that matches the business name.