To me there are punishments that should be a learning lesson, and then there are punishments that are for play.

A sub who is good at word play and gets a good jab in, my reaching out and tweaking a nipple in response to the teasing could be considered punishment, but to me, it's not a negative punishment, its a play punishment. Or maybe you get the sub all turned on, feel her pussy and how wet it is, then bend her over your knee, "Bad Bad slutty girl! your pussy is very wet!! you need a spanking!" See where I am going with this?