[1] This block of addresses is specifically meant to be used by Internet service providers (or ISPs) that implement carrier-grade NAT, to connect their customer-premises equipment (CPE) to their core routers.
If an ISP deploys a CGN and uses private Internet address space[2] (networks 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) to connect their customers, there is a risk that customer equipment using an internal network in the same range will stop working.
This prompted some ISPs to develop policy within American Registry for Internet Numbers (ARIN) to allocate new private address space for CGNs.
ARIN, however, deferred to the Internet Engineering Task Force (IETF) before implementing the policy, indicating that the matter was not typical allocation but a reservation for technical purposes.
Its main purpose was to postpone the depletion of IPv4 addresses, by allowing ISPs to introduce a second layer of NATting.