What I find is this. Spanking is most effective in dealing with young children. They fear being spanked. The spanking gives weight to your words. The spanking sobers and humbles the child. As children get older they get more stoic about spanking. They learn how to deal with it. The intensity of spanking required to make the same impression on a 12-year-old that you make on a 2-year-old would be excessive.
Not always and not completely. Speaking from experience, I do not remember the reason why I was spanked, just that my father spanked me. It certainly humiliated me and seriously discouraged my spirit.
