I agree in principle, and some of the stuff sold as “parmesan cheese”, such as the Kraft stuff that sits on the shelf unrefrigerated, is indistinguishable from sawdust. However it’s possible to get good quality pre-grated Parmigiano-Reggiano and I just find it more convenient, plus the machine-grated stuff tends to be finer and more suitable for many uses. The stuff I buy is grated in the store from good quality imported Parmigiano-Reggiano and comes with a label showing the brand and the various attributes of the cheese it was grated from.