About the spanking post, yes it is correctional. In some dom/sub relationships the submissive gives a lot of control over to the dominant. This means that they establish rules and behaviors the sub is supposed to adhere to. So, for example if the sub is supposed to address their dom as sir and they forget. The first time they'll usually be warned, but the second time they'll be punished. Completely consensually, the sub wants to be punished. They want to behave for their dom.