It’s critical because its proper outcome is a machine that boots and runs when that operation is complete, the old drive removed, and the new drive put in its place.

Such a cloning operation becomes critical on Windows PCs when the drive to be replaced is the boot/system drive, meaning it contains the files used to boot up the machine when it’s starting up or restarting, as well the operating system files used to run Windows itself. Cloning a PC drive comes in handy for a variety of reasons, but primarily when you want to replace one drive on a PC with another that is either bigger or faster than the original drive, if not both.