One thing that struck me when reading up on Cassandra is that there is a very strong mindset in the Cassandra community around linear scalability and therefore on primary key based data models. So de-normalizing your data, such as by using materialized views is considered a best practice.
However, de-normalization has some challenges of its own. Both Cassandra-managed materialized views or any other application side managed denormalization run the risk of becoming inconsistent. And of course it does mean you're multiplying your database size.