Every piano (upright or grand piano) has its own "secret measurement" from different piano manufacturer. a well regulated piano will produce a good aftertouch. a bad regulated piano action will generate weird touch, unnecessary noise, double knocking, key jam etc.
some pianist will prefer a firm touch and some prefer a softer, a professional technician is able to regulate or alter the touch according to their preference by setting the distance, height, weight and other measurement.
To regulate a piano is a time consuming task and must be performed carefully by an experienced piano technician.
how often do we need to regulate the piano? well depend on how frequent and heavy you use the piano
. it is just like driving your vehicle, the more and longer you drive, wheels alignment will likely to go off.
upright piano action
grand piano action