I always bring at least one mouth reed when hunting elk after the rut. I don't expect to call in an elk, but cow calls can calm elk that are about to spook. It can also stop them as they are slowly moving though an area. A couple weeks ago on a cow hunt, my hunting partner and I glassed up a few cows at 800 yards, and they were moving away from us. I blew a couple cow calls, and they all stopped. We put together a quick plan where he would work around some timber and ridges to get close enough for a shot. I would stay on the glass and blow calls if and when the elk began to move. Over the course of the next hour, he made a circle and got into 350 yards. I blew calls every time the elk started to move. Over that hour the elk moved about 100 yards laterally to us, and my buddy was able to kill a cow without them ever knowing either of us were in the area. Without any calling, those elk would have continued to move away from us, and we never would have had a shot.