Its been seen that some folks would like to use zookeeper for very fine grained locking. Also, in there use case they are fine with loosing all old zookeeper state if they reboot zookeeper or zookeeper goes down. The use case is more of a runtime locking wherein forgetting the state of locks is acceptable in case of a zookeeper reboot. Not logging to disk allows high throughput on and low latency on the writes to zookeeper. This would be a configuration option to set (ofcourse the default would be logging to disk).