It's not necessary, but it might be necessary for the child to believe that's a possibility. It's like armies. The presence and the possibility do most of the work. My grandfather didn't beat his children, but e.g. spanks and being hit on the butt by a belt were permissible by society. He didn't do that AFAIK, but the children knew it was possible, and a single look from him sufficed to get them to stop misbehaving.
He's very loved by them, BTW. I didn't meet him, but they always talk with admiration of him.
It might be like brakes. Some people abuse the brakes for their own self-satisfaction to e.g. brake-check others, others brake hard every time they need to come to a stop (e.g. intersections) because they don't know otherwise, and then others make it seem like the brakes don't even exist as the car glides without disturbance to the point that you might find it normal to have a drink from a open cup throughout. It's always necessary to have the brakes, and always permissible to slam on them in case an emergency is happening, but they're ideally used sparingly and softly. They should ideally be made to seem like they don't exist, even though everyone knows they do.
Dude, you're breaking the analogy. Imagine an ICE car from the 90s. It's not about what technologies you're using. It's about the skill and intent with which you use the brake pedal (considering it the only form of braking).
Can you elaborate on how Billy's dad would make sure he never threw rocks at people again?
FWIW, I grew up in the Midwest in the 80s and was subject to corporal punishment. Also witnessed only the black children being spanked at school in the South Eastern US.
Sure - having raised kids myself, and never once hitting them, there are lots of ways to memorably punish a kid. First and foremost, kids really respond when their parents get upset. They remembered when I was visibly angry with something they did. Throw in some "I am so disappointed with you" from the other parent, maybe grounding them or taking something away they want, and we have something a kid would like to avoid in the future. Like any punishment, it can't be used too much or it loses effectiveness (so if you blow up at your kids constantly all you are doing is funding a future therapist's income...)
FWIW, teachers in my (basically all-white) school in the Northeast US in the 70's and 80's would occasionally paddle kids for egregious behavior (like doing something dangerous or open insubordination.) In my low-N observations, it had dubious effectiveness. Kids who were generally good but just messed up once appeared to be "scared straight", although of course I can't say if it was more effective than non-corporal punishment. The sudden shock and embarrassment of being paddled seemed to be effective though. If the kid was a "behavior problem" paddling wouldn't fix the underlying issues.
Also, if you were punished at school, you could expect to be punished at home, if your parents ever found out. Most parents back then would immediately side with the teachers; that's something else that has really shifted in the last half-century. Today, parents are involved to the point of interference, at least in the more affluent areas.
He's very loved by them, BTW. I didn't meet him, but they always talk with admiration of him.