What exactly is the advantage of 11 pin MHL connector in Samsung Galaxy S3 I have read that samsung galaxy S3 has a 11 pin mhl connector and it can support USB OTG as well. Also I have read that the device can power the cable. I didnt quite get what is meant by USB OTG support included. Both MHL and USB OTG are there on other phones too (like sgs2 and htc one x). How do I use the 11 pin connector to my advantage?

Also if the 11 pin connecter can power the device, then why do we need to again connect power cable to the mhl adapter provided by samsung?
USB OTG stands for USB On-The-Go. This allows your phone to use USB devices (e.g. mice, keyboards, external USB drives) through a MicroUSB to USB adapter.

The MHL adapter allows your device to connect via HDMI to a TV or monitor. The statement that it can power the device just means that it can both charge/power the phone and allow HDMI output via the MHL adapter.  To get that power, though, it requires your power cable to be connected, as HDMI does not provide power. Not all MHL adapters can do this.