> The primary reason is that it uses all of your computer's available cores to walk through directories and copy files, effectively speeding things up by a fact

> The primary reason is that it uses all of your computer's available cores to walk through directories and copy files, effectively speeding things up by a factor directly proportional to how many cores you have. CPU cores can't read/write files, those are IO operations by the storage device. The CPU could have 64 cores but on a system with a single hard disk that can do just one concurrent operation.