The related conversation on the zookeeper user mailing list is here - http://apache.markmail.org/message/4jjcmooniowwugu2?q=+list:org.apache.hadoop.zookeeper-user
It is useful to be able to monitor the number of disconnect operations on a client. This is generally indicative of a client going through large number of GC and hence disconnecting way too often from a zookeeper cluster.
Today, this information is only indirectly exposed as part of the stat command which requires counting the results. That's alot of work for the server to do just to get connection count.
For monitoring purposes, it will be useful to have this exposed through JMX and 4lw srvr.