Information can only be moved over a network in a binary format, which (in Java terms) means that the objects (the data) need to be serialized. Outside of one special case (an advanced programmatic option called the "object backing map"), the servers always store the information in a serialized form, so that the information is ready to go "on the wire". Additionally, using indexes, the servers can also store various parts of the information in their deserialized form, which speed up server-side processing (queries, entry processors, aggregators).
Caches on the clients (called "near" caches) are managed in the deserialized form, so that data cached locally does not need to be repeatedly deserialized.