Why would one do this? What would it show? Has it happened to you?
Training with people from other arts is a great way to test one's assumptions, with a particular eye to finding blind spots in one's own training. Many possible lessons are available, but the ones most relevant to the post I was responding to include:
* The realization that good attackers don't actually unbalance themselves much, if at all, when they attack. This challenges the assumption that the energy of an attack makes it "easy" to unbalance the attacker.
* The realization that actually completing an irimi entry against a non-compliant attacker is not a trivial matter, and potentially creates many opportunities for reversals and followup strikes.
* The realization that merely getting behind someone does not, in fact, necessarily give you control of their balance.