Depends on the level of training of the horse , of course, but I never hang onto my horse's mouth constantly, even lightly to rate speed. I will correct them, by taking contact, firmly, but then get 'out' again.
Far as the backing, it is not the only way to teach a horse to stand, but I don't either wish to ride little circles, when a horse won't stand-i want that horse to stand.
The reason I use backing, is to get that horse off the bit. A horse trying to move off unasked, will also be leaning on that bit. If you just try to hold a horse in a stop, using the bit, the horse will either get more up tight, maybe try to toss head, even go up a bit, or just figget around
Thus, the back I use, is not the saft cues I use, asking fro a backup in some class, or on a trail course, but it is a correction, where I take hold of that horse, trying to move off, and then really bump him several times with my legs-hard, backing him just enough until he is off that bit, , repeat whoa, and give him slack again, expecting him to do the 'right thing', and that is to stand there, on a loose rein, until asked to move
I guess you could also kick his hips around, taking his head to the side, and then ask for that whoa. The point being, not standing for that whoa, has to become the hard and wrong thing, to make that obedient whoa and standing there, the easy and right thing to do
Yes, I expect my horse to accept any place in line, but you can also ruin horse that naturally walks out nicely on a trail ride, the type of horse you want, and something desirable in a trail horse, by forcing him to go at the walk of some horse dragging himself slowly down the trail.
This is not the same as teaching a horse to rate his speed in a show ring, so you avoid constantly passing horses, thus looking like your horse can't have his speed rated. In a show ring, you can ask your horse to move deeper, more collected, which will make him more slow legged, thus covering ground slower
I don't do that on atrail ride. If ahorse tries to go to a trot, from a walk, unasked, to pass another horse, that is a different thing, then that horse just having a nice long stride ata walk, covering ground-something I encourage, not discourage!