My TV only has one HDMI port (it's quite old now!), so needed a switch box to connect the BT Vision box, XBox and whatever third device I add.
No fancy set up, just 1 output and 3 inputs. There is an option for an external power source (not supplied), but I've not found I've needed one yet.
Only down sides:
The blue LED indicators to show which source is in use, is a bit bright... Blu-tack will sort them!
The inputs and outputs are located on the sides of the box with the IR sensor on the front.
But lets face it, it did only cost £8!