Actually, it's not that silly.
It's silly if you try to use it for debugging or building as if it won't affect the running game, but it's handy for other purposes.
For example, one idea I had a while back was to have the "main" port only accept new characters, and a second port only accept existing characters. When you log into the advertised port, instead of asking for a username, it throws you into character creation -- which in my idea was the middle of a battle, where the choices you make in resolving the battle determine your character type. Then you talk to one of the surviving npc's to learn about the game and provide your name/gender/etc data.
At that point, you enter the newbie zone proper, where you can wander about, chat, kill small things, keep yourself amused until an admin approves your character and gives you a key to pass into the real mud. Once authorized, you can log in on the second port to avoid having to tell the mob that you've been there before.
That's the kind of thing you can't easily do with a single port, because to have enough atmosphere to make it entertaining, it would be painful for people who just want to log into their 40th level character... By only allowing existing characters on the second port, you ensure that everyone goes through the newbie area (and thus sees what you think they need to see) at least once.