It's pretty much the same as a check in desk, except it is located after security and those expected to use it are people who transfer through the airport. So, if you arrive on one flight and are going to leave on another, and you have not checked in for your onward flight, then you would need to use the transfer desk to check in for that flight and receive your boarding pass.

Normally you can receive the boarding passes for all your flights in a trip at the time when you check in for your first flight, but sometimes that may be impossible for some reason. Using the transfer desk means that you don't have to exit through immigration and customs, check in, and then pass through security again.