The client contacts the server merely to maintain the integrity of the cache, as directed by the TTL value in the config file.  The 2.1 server also returns key status/attributes so the client can determine if a key has been marked as compromised etc. (You would also need the 2.1 client R_KM_KEY_get_by_xxxx API to extract that information.), so this behavior is a lot more useful in 2.1.