What's the advantage of the inet datatype in Cassandra vs a plain text string?
It's a special datatype for storing ip addresses. It would be more compact that the string representation of the same information as well as type safe.

inet    An IP address. It can be either 4 bytes long (IPv4) or 
16 bytes long (IPv6). There is no inet constant, 
IP address should be inputed as strings


https://cassandra.apache.org/doc/cql3/CQL.html