creating a client-server TCP connection in node : socket.io or net module

I'm newbie to node and I would like to create a TCP connection between client and server using node.js. I already have an http server built on node and which sends/pulls data to and from the client. Now, I need to add this 'connection' oriented concept.

I've been reading tutorials and forums and I'm little confused. If I understood well, there are two ways of creating such connection:

• upgrading my already existing http server to a socket.IO server

  var app = require('http').createServer(handler);
  var io = require('socket.io').listen(app);
  function handler(req, res){
     //code
  }
  app.listen(8080);
  

• creating a separate TCP server based on net module then establish a connection between this TCP server and the http server like is suggested here Create WebSockets between a TCP server and HTTP server in node.js

  var net = require('net');
  net.createServer(function (socket) {
     socket.write('Hello World!\r\n');
     socket.end();
   }).listen(1337);
  

So, when do we need to create 2 separate TCP and HTTP servers and when do we need to have only one server (upgrade an HTTP server to a socket.IO one) ?