Capped connectivity solutions are usually based on dynamic IP addressing, which means that a computer is assigned a different IP address each time it connects to the Internet. This “dynamic” addressing is convenient in that it allows mobile computers to move between different networks more easily.
With a fixed IP address, however, the same IP address is assigned every time. This enables a computer to be more reliably reached over the network by its host/domain name.
Using static IP addressing for devices on a network helps to avoid potential conflicts. For example, dynamic naming protocols sometimes supply an address that has already been assigned statically elsewhere.