My son and I have had a great year with close encounters on big bucks. A huge part of that has been grunting. Both of us agree that we never heard bucks as vocal as we have this year. He had one encounter with 2 mature bucks that he compared to calling turkeys.....they would grunt, he would grunt, they would answer.
My take is this;if they are rutty, a grunt call can make all kinds of crazy stuff happen. If they aren't a blind grunt every once in awhile can certainly get the attention of a buck in the area. A buck off in the distance? Give it a shot, it works quite a bit.
One of my favorite uses of a grunt call.....everyone talks about big bucks "going nocturnal". That's debatable but I do agree that a mature buck is first in last out of a bedding area. Using my Lone Wolf, I hunt closer to thick bedding areas than most folks. I have used a grunt call successfully to get a buck to just stand up....a buck I had no idea was there. Interesting when bow hunting, deadly when gun hunting.