Calibration is used to maintain standards in assessments. It is also used to ensure that assessments are valid tests of the required skills. For any cognitive test used in recruitment to have validity, it must be calibrated. The assessment must be completely relevant to the skills required for the position, or the results will be invalid for use in recruitment.
Most assessments are calibrated to allow for variation. When you calibrate a test score for variability, it is then known as a derived score. This is the type of score that you will get from most of the best well-researched cognitive assessments.