The calibraton function does not serve the purpose of adapting the sensor to low power IR light sources nor does it in any way influence the communication with the Wii Remote or change its settings in any way. It is purely a function of the driver, which should only be used if you can not reach one or more borders of your screen.
When in mouse mode, the position of the mouse pointer on the screen is determined by where the sensor field in the front of the remote recognizes the infrared light source. If objects are hindering the path between remote and sensor, the borders of the screen can no longer be reached.
This is exactly where the calibration function kicks in. Using it, you can intuitively determine which area of the sensor should be used to interpolate to your screen coordinates. Therefore, start calibration and follow the instructions on the screen. The goal is to maximize the size of the rectangle on the screen with your movements.