If a cable breaks the elevators will be floating and trim will work. This is clearly documented in the POH along with other factors affecting pitch such as flaps. This procedure should be regularly practiced and trained for. We were aware of this and practiced it in Africa but that was a long time ago. I doubt is standards have slipped in the meanwhile but.......
The danger is a cable break at low level with little time to respond, if the aircraft is fully trimmed at all times you have a chance, if you fly with pressure on the yoke it can all go wrong very quickly.