Another case is you have departments in your company like: HR, payroll, sales, info, etc. - MRG Digital Websites and Hosting MRG Digital Creating Custom Websites and other Services

You currently have an employee that does sales correspondence but she will be retiring in a month what will happen in that transition? Lets look:

lost mail do to no one else checking the email - maybe no one even knows the password!
you need to change all your advertising to a new address and it may only be a temporary one so you will need to do the process all over then just to find out someone didn't get the new info and sent it to the old address because they had a business card from 10 years ago.
- What if you had it set up in a way that you were advertising a contact email of but it goes to your current employee of then when its time you can change it to because they don't want another username and password to keep track of and it goes into a folder just for work information.