I used to hit my kids (for serious things, like playing with fire) but I saw that it does not work, so I stopped.
Now, I only hit when i’m angry (just kidding!!).
Withholding a privilege is far, far more effective, less treats on Shabbos or something like that… boy do they remember for a long time! One of the reasons is because they think about the punishment from when you tell them, until you carry it out.
They would gladly trade a potch and get the privilege back – which shows what is more powerful!!
The only time i hit is for a little kid (eg. 2 year old) who plays with the gas-stove / electrical / runs in the road. At that age even a small smack is VERY effective, to associate a certain behavior with punishment.
(Often, it does not need to hurt the kid, it’s more the embarrassment, or they fact that they’ve let you down.)