If you have a pool consisting of a single device (such as a drive in a laptop) the second copy could protect from loss of a file that includes storage that can

If you have a pool consisting of a single device (such as a drive in a laptop) the second copy could protect from loss of a file that includes storage that can not be read. In a multiple device pool (with some redundancy) it would IMO be a extra and unneeded layer of protection.