Well the reason why some people buy bitcoin addresses is, they want to check there some clamcoins especially if the address had bitcoins held on May 12,2014 or if your address had some forked coins like bitcoin cash and other bitcoin forksthere are some sutes like freebitcoins.com where you can check your address if there are some forked coins or clams in there or a service like LoyceV wallet digging service.