I think the rule of thumb people can use is, if the helper is doing this with more than one dog, ( or all the dogs in the club), and doing it all the time, you can start to suspect that he might not know what he is doing, or is simply going thru the motions. Each dog is different and there are other ways to calm a dog, or disturb them, through the helper work without touching him with your hands. Last dog I did that with was a very nervy female malinois. I did not do it to calm her on the grip , I did it after the rest of the work achieved that and only briefly, mostly because I was so impressed by the transformation of that dog and wanted to see if she would allow it, when before that point, she would have completely freaked out. I don't recall doing it before that dog, that's how infrequently I have done it.
I see people do this now where the hand is on the top of the head and under the chin. Some seem like they are actually holding the dog's mouth on the sleeve. Again, proper helper work will achieve the result where the dog will hold, trying to do it with "obedience" is just dumb. I see people doing this with lots of dogs, not really in a specific fashion and that right there tells me all I need to know. . Not something I believe in , especially as I have said, the people doing it are, with every dog they work. I've had people ask me to do that stuff and I don't feel any difference in the grip. Don't really believe in using it to pressure the dogs so, that could be part of the reason...but I doubt it. The most effective helpers apply and release pressure or disturb the dogs more through mental pressure than any kind of physical contact. Not many people have the ability to do it, so, these are the things they use...too often....if you ask me and it will not take the place of the later. Touching the dog can be just as "rote", when it is done over and over in training.
It is also, when done correctly and at the correct time, to check the grip. Not only the fullness, but the intensity and chewiness. A grip might look full, but the pressure is "like a butterfly on my arm" .
I have never had to feel the grip with my other hand. If a helper has to do that, they should not be working dogs. Maybe you meant something else Sue? That makes no sense to me.
Yes, you should always ask a helper WHY. Seems like many helpers just get stuck doing the same stuff whether it produces a result or not. They just do it, to do it.