I believe that they are doing the cutting to keep the car driving the same at the end of the race.
I understand your question. Afterlavera. If the roll out is the same then they are going to wear at the same rate. I myself dont understand why they would want to make it harder to set up the car for each run. I dont true my tires each run. I can run the same set of tires all day. Start with 63mm and make the 3 quals and 20 min main. All I do is rotate the tires left to right each run. It works for me. The car never feels odd to me. I also might be the surface they are running on is more abreasive then some.
Each person has thier own way of setting up for the race. Its interesting to see how each person does it. But if it works, awesome.