I used to repair iPhone screens and can answer this. It was the easiest way to check the device worked after the repair and that the screen didn’t have any dead

I used to repair iPhone screens and can answer this. It was the easiest way to check the device worked after the repair and that the screen didn’t have any dead spots. We told people to wipe the phones before they brought them in, and gave people the option of either giving us the PIN code or accepting the device back without us validating the fix. I don’t think I ever had a single person say no to the pin but we did have plenty of people wipe the device before they brought it in.