Labs all use scan data to establish their symmetry and cut grades. GIA use the proportion data and a look up table the same way that HCA and the HCA app function. The American Gem Society (AGS) use a 3D model of the diamond to estimate the diamonds potential beauty using its proprietary data base (AGS PGS) that estimates various light performance and other factors.
GIA also uses the data it collects to "finger print" diamonds in its Horizon program to screen for resubmitted diamonds; e.g. dealers hoping for a better grade.
There can be variations in HCA results based on the accuracy of the scan data.
Sample of the Sarin Report
Sarin cut optimisation software