Also it would be nice to know (document/specify) whether setting new addresses/a new result on the listener will cause automatic connection attempts to those addresses or if they will only be used on demand.

It's unspecified, so it is up to the particular loadbalancer's implementation.

So can I interpret this as "avoid unnecessary calls to the Listener#onResult() method"?

The name resolver implementation should avoid unnecessary calls to Listener#onResult() if nothing is changed from resolver's perspective. The name resolver should not assume that the listener implementation will do a refresh connection and should not try to achieve that purpose by calling Listener#onResult() multiple times with exactly the same result.

If you could add that to the javadocs of the class/method that would be perfect.

Maybe there should be a OnlyChangeForwardingListener in the API that only calls the underlying Listener if the result changed from previous calls. That way we don't have to implement the feature every time and you could also use it in the internal implementations such as DNSNameResolver. Although I would prefer it, if grpc-java would explicitly wrap the listener in it before passing it to the NameResolver.