For the same reason that thermal calibration is performed — to ensure that the light’s internal sensor measurements correspond accurately to the true values. Take a measurement, then apply the configuration.
It was a feature added to Anduril 2’s advanced UI, and allows one to apply a correction factor as needed, via an additional 7H click sequence when in the battery check mode.
The T2 has piqued my interest, but too bad about the tint, proprietary cell, and price.