Além de ser o principal uso na Internet, outro grande uso para isso é a segmentação de intervalos de endereços IP privados para grandes redes corporativas
RFC1519 diz
Classless Inter-Domain Routing (CIDR):
an Address Assignment and Aggregation Strategy
1. Problem, Goal, and Motivation
As the Internet has evolved and grown over in recent years, it has
become evident that it is soon to face several serious scaling
problems. These include:
1. Exhaustion of the class B network address space. One
fundamental cause of this problem is the lack of a network
class of a size which is appropriate for mid-sized
organization; class C, with a maximum of 254 host
addresses, is too small, while class B, which allows up to
65534 addresses, is too large for most organizations.
2. Growth of routing tables in Internet routers beyond the
ability of current software, hardware, and people to
effectively manage.
3. Eventual exhaustion of the 32-bit IP address space.
It has become clear that the first two of these problems are likely
to become critical within the next one to three years. This memo
attempts to deal with these problems by proposing a mechanism to slow
the growth of the routing table and the need for allocating new IP
network numbers. It does not attempt to solve the third problem,
which is of a more long-term nature, but instead endeavors to ease
enough of the short to mid-term difficulties to allow the Internet to
continue to function efficiently while progress is made on a longer-
term solution.