The OP really needs to distinguish between "smacking" or "spanking" and "beating." Beating, when I've ever heard it, refers to repeated harsh hitting that constitutes child abuse. So that was the first image I got here: is child abuse okay?
Anyway, semantics aside, I was spanked as a kid. It sucked, but y'know, pain sucks, and I'm pretty sure I hated the mental pain of getting reprimanded more than I hated getting spanked. (I was one of those OH NO YOU'RE DISAPPOINTED IN ME THE WORLD IS ENDING kids) Still, it taught me really quickly that Parents Are To Be Respected. I agree with Xanian that part of the key is, don't do it out of hate or maliciousness, do it out of "look, this is what will get your attention." Don't be emotional about it.
Caveat: I don't like kids and never want them, so I'm probably not the best to answer, but the Internet is all about giving opinions, so here goes. I think that in general, pain is a very good teacher. It is a fundamental biological trigger that tells your body to quit doing what it's doing -- see how you put your hand on a hot stove and really regret that a moment later. When you yell at a person, or try to have a discussion, they can argue. If your goal is to get them to listen to you unconditionally (don't punch your brother in the face, let's say, because in 99.9% of cases this is a terrible idea), then you don't want to give someone a chance to argue or fight back. Associating "bad thing" with "pain" seems like a pretty good way of conditioning someone to never ever do a bad thing. You can't argue with pain, and it invokes the primal response of "stop now." Hell, I went to a school where the kids were Paragons of Morality because the principal had an old wooden paddle and everyone seriously believed that he was going to use it. (Not sure when the laws against that went on the books, so it could have been very much true. Anyway, it was effectively true because everyone believed it.) It honestly really did work.
Of course, as even cats demonstrate, the solution to this for the punished person is to just do it when no one's looking, but that applies no matter what method of punishment you use. Eh.
Anyway, semantics aside, I was spanked as a kid. It sucked, but y'know, pain sucks, and I'm pretty sure I hated the mental pain of getting reprimanded more than I hated getting spanked. (I was one of those OH NO YOU'RE DISAPPOINTED IN ME THE WORLD IS ENDING kids) Still, it taught me really quickly that Parents Are To Be Respected. I agree with Xanian that part of the key is, don't do it out of hate or maliciousness, do it out of "look, this is what will get your attention." Don't be emotional about it.
Caveat: I don't like kids and never want them, so I'm probably not the best to answer, but the Internet is all about giving opinions, so here goes. I think that in general, pain is a very good teacher. It is a fundamental biological trigger that tells your body to quit doing what it's doing -- see how you put your hand on a hot stove and really regret that a moment later. When you yell at a person, or try to have a discussion, they can argue. If your goal is to get them to listen to you unconditionally (don't punch your brother in the face, let's say, because in 99.9% of cases this is a terrible idea), then you don't want to give someone a chance to argue or fight back. Associating "bad thing" with "pain" seems like a pretty good way of conditioning someone to never ever do a bad thing. You can't argue with pain, and it invokes the primal response of "stop now." Hell, I went to a school where the kids were Paragons of Morality because the principal had an old wooden paddle and everyone seriously believed that he was going to use it. (Not sure when the laws against that went on the books, so it could have been very much true. Anyway, it was effectively true because everyone believed it.) It honestly really did work.
Of course, as even cats demonstrate, the solution to this for the punished person is to just do it when no one's looking, but that applies no matter what method of punishment you use. Eh.