If I see this correctly I find that there are two major ways in which punishment is used in bdsm:
It is used to, and I quote Ragoczy (in a post that gave me inspiration for this thread),
In this case punishment should not be enjoyed by the sub, because obviously the sub should learn from it and not want to be punished again.correct an undesirable behavior
But on the other hand, punishment is seen as part of a roleplay where one (acts that he/she) has done something wrong and therefore has to be punished by the Dom(me). In this case the punishment is often something the sub enjoys like being tied up and spanked.
Probably everyone has his/her own vision about punishment, so I'm wondering how do you use punishment?
I don't really see why people want to use punishments that the sub doesn't enjoy, because that would take the fun out of the play, wouldn't it? Or maybe it is just my vision that it should be fun for both.