The question remains, how effective is hitting in general as in applied to all situations, your kids, random strangers, and what not.
Fear is quite the motivator, it leads to the dark side and all.
The thing is, you can still get the same effect without striking with pets. A bottle of water to spray at a cat or dog, a high pitched electronic device triggered by you, or even in extreme cases shock collars.
Now, I am not frr any of these methods. However, when you are dealing with pets, the English language tends to fall on deaf ears. Sure, they might understand their name when you call it enough times. Sure, they might learn the word Good when things are going well, and they learn NO and BAD and associate it with the negative reinforcement. But short of that, you can not explain to the animal "Mister Fluffers, would you kindly stop pissing behind the TV please?"
So there in is the problem, if you can not communicate, only physical interactions become the speech. But would you rather you pet not piss on the carpet because he respects you or because he is afraid you will beat the shit out of him?