How 1 or Many ports on a Application

Hi Everyone!
I wanted to get an opinion from everyone on when building a small to large applications that is in one self contained binary is there any benifit to useing multiple ports instead of just one port?

For instance if I where to build a application that allows you to Chat and Send files would there be any real good reason on why i shouldnt do it all on the same TCP port if I can handle it being a File or a Text message on the Session layer 5 level, I'm thinking just requiring more ports open will just make configuring a Firewall more annoying but is there a software limition on a single port I may not be aware of?
Thanks,
-Agent

Consider the fact that web servers, even extremely high volume web servers, send and receive all their traffic on port 80. That's a pretty good indication that you should use just one port.

Fair enough. I figured that was the case.
Thanks,
-Agent :)