Yeah, but when you hand over a book, all your other books are still available to you.
As are the Kindle books on the device. 'Copies' are available for you to read on all compatible devices, up to the number of licenses allowed by the publisher. If that happens to be six (very common, some are unlimited...however, textbooks may be limited to one or two licenses), six people can read the same book, on six different devices...at the same time. Not feasible with one copy of a physical book.