Having the 3 DNS entries point to the 3 different port numbers on your
server, all using the same IP address, means that your URLs will
definitely have port number in them. Some people don't like this,
they want their publically visible URLs to look like
"http://www.mysite.com/" not "http://www.mysite.com:9001/".
I'm not sure whether there are any other drawback or not. (For
example, SSL certificates.)
