One major advantage over ssh is that krb5-rsh has much lower latency
and overhead (in terms of used cpu time) when executing a plain
/bin/true on a remote host, doing that in a loop over 1000 logins can
take hours with ssh but takes minutes with krb-rsh. ssh is a *major*
pain in the arse if you have a distributed cluster which depends on
rsh/ssh - with ssh the cpu time overhead is so great that it often
doesn't even make sense to call the remote host to offload a job.
krb-rsh is much more lightweight, e.g. consumes much less cpu time.