Calibrating the height of the platform enables the machine to know the Z-axis height of the platform, which may vary each time you reinstall the platform.
The platform height, in combination of the thickness of the material and the focal length (which is fixed for the 10W/20W/40W Laser Module), allows the machine to determine the appropriate height to raise the toolhead during laser machining. This can ensure that the focal point falls right on the surface of the material, which in most cases can guarantee optimal engraving and cutting results, making auto-focus possible.
Therefore, if you want to auto-focus the laser through the Input Material Thickness mode, you need to calibrate the platform height first.
Every time you reinstall the laser platform, you need to re-calibrate the platform height. Otherwise, the results of auto-focus may be inaccurate.