However sometimes it just doesn’t make much difference. The lighter framed birds can be quite determined fliers however much you trim them. Also some people leave the wings alone as they believe if a predator was to attack it would give the hen a better chance to escape.
It’s a procedure that should be done with care as you can catch there are blood vessels that run through parts of the wing. You should only trim the flight feathers of one of the wings, not both.