Pain isn't the worst punishment and often it can be used to enhance the pleasure, to wake nerve endings in places ordinarily not associated with sex and submission - so that it is all of you that submits, not just the nipple that is clamped or the deep ache that is nurtured.

For me it helps focus my mind, as somebody else pointed, to block out the room, the outside noise, the things in the room and when it hurts to fix on my Master and what he is telling me to do.

The worst punishment is, I agree, him walking away from me in disgust, or disappointment and leaving me there. To not have him near me, or pleased with me.