For the snaffle bit, the hands are brought more toward the horse’s hip. Most people can put steady pressure on the snaffle bit rein, and the horse will likely give to it at some point. Conversely, if you put steady pressure on a hackamore, the horse is likely to learn to push on it.
Knowing how the snaffle bit works is helpful in... MORE developing effective rein aids, and avoid either being ineffectual or too hard on your horse's mouth. Although the basic action of most snaffle bits is the same, it sometimes takes trying a few different bits to find one your horse is comfortable with.