We almost lost our tow'd 4 down a few years ago. When I pulled into a campground as we were returning from Alaska I noted that the hitch was at a "funny" angle (any angle other than straight being funny). When I examined it more closely with a mobile service tech we saw that the several of the welds holding the receiver to the coach were cracked. Had they let go the car would have gone off on its own playing pole vault over the towbar and the breakaway cable and the safety cables would have still been fastened to the receiver no longer fastened to the coach. My fully installed break away system would have been useless.
Not to get into the to have or not to have auxiliary brakes in the tow'd, but I can feel the difference when braking hard even in my 30k lb coach with airbrakes. Every bit of assistance is welcome when the idiot crosses in front of me.