I have heard discussions of this topic on fetlife, and thought i would expound here instead of on a forum post, so here goes.
Does the slave retain any or all power when they surrender it of their own free will? Short answer: no. Long answer: no with caveats. The simple explanation is that if you keep a sub/slave happy, they will strive to make you happy. A slave who isnt valued as a person or whose opinions truly dont matter to the dom will likely become listless over time, and their lack of effort will cause strife that may lead to a split.
I, for example, am not a physical sadist. I have heard doms that say because of this that I am not a real dom, but I'll happily tell those where to stick it. My girls all give me the credit for my position, and that is what matters. I know what I am- I operate on the mental plane (it is so much more powerful). Instead of beating a slave into submission, I prefer to herd them into giving it up willingly. I think all slaves crave this being done, at least to some extent.
One of my girls, a bona fide pain slut, has experienced this. She was in a relationship where her Master was entirely concerned with the physical. So why would a pain slut become dissatisfied with this arrangement? its because she craved the mental arts, which she never got in that relationship.
An eqqually valid question is this: I do not enjoy the physical, but I have two pain sluts that couldnt be happier...why? One of these pain sluts has been with me for 10 years and there is no dissatisfaction between us. Why?
The answer is mental. Even with the newer pain slut, I have such a tight grip on their minds that they couldn't imagine not being with me. This is why I believe that mental arts are so effective.
Do they, or my third, a rope slut, have power? No. They will bend to my will whatever the cost. However, comma, if I ignored their wishes altogether they may become dissatisfied. So, despite my indifference to the physical, I indulge their physical masochism from time. This brings me back to the main thesis.
The slaves have no power to get me to do this, in my view. I indulge the physical when I feel like it, not when they do. But by indulging them on occasion, they don't have to completely give up that desire for a good beating totally, and they get good value in exchange for total physical fulfillment- total mental domination and manipulation, and there is no doubt that I care for each of them and provide them protection from whatever comes, physical, mental, or emotional.
In the vanilla world, I also see my slaves as people in their own right. When a decision needs to be made, my decision is final- the difference is that I get the slaves' opinions on the subject. I may decide against them, but the fact that I take their view into account gives them a sense of really being important to me, and each of them is.
You see, it's not that they have power, but that I step out of my comfort zone sometimes to indulge them, thereby keeping them dedicated. If my newest girl's former Master had paid a little attention to the mental and emotional, he would still have her. Since I care for my girls, controlling them mentally, giving them physical pain once in a while, listening to them, and being the steady, reliable presence for them, they are so happy that they will go far out of their way to please me. This is the secret to a good M/s dynamic. Even a pain slut needs the full package of domination and to feel that she is valued as a person to be happy, my newest is proof of this.
If you dont earn the title Master from the slave, of their own free will, you are not a Master. And you would be surprised how little pain it can take to physically break a pain slut. Perhaps I will expand on this idea later in its own topic.