Stop/Don't Stop

Husband and I have been married for almost 16 years. We've been a couple for even longer. I think that's a long time in anyone's book.
And yet I still don't always understand how his mind works.

Sometimes he wants me to beg for more. My cries of ecstasy clearly drive him on, especially when he's doing something sexually charging, like rubbing my clit or spreading me wide open to wiggle his fingers inside. He also wants to hear my pleas for more when he's flogging me, or spanking me, or just abusing my flesh in some other way. He wants to hear the resonance of pleasure in my voice from his meted pain.

Other times, he wants me to beg him to stop. I have my safeword, (which I have used on occasion,) and he knows unless I use my safeword, he is free to continue to play with
(hurt)
me. He uses this knowledge to his advantage. Often he brings me to tears of pain. When he can, when opportunity arises (i.e. when we don't have to worry about the kids), he loves to hear me scream. Which is good, because I am a screamer. I love to scream; I love giving in to that fear. But that's the subject of another post.
He'll keep walloping me until I'm screaming in agony, begging him for mercy. Of course, he offers none.

I don't know why sometimes he wants to hear me beg him to continue, and other times he wants to hear me beg him to stop. And I don't know what it is that makes him switch between the two extremes, often many times in the same night. One minute, he might be flogging me steadily, rhythmically, using an even strength, lulling me into subspace and listening to me moan in contentment. The next minute, he'll be picking up the brush and beating me with it so hard, I want to leap out of my skin.

Are all Sadists like this? Do they all have their own unique cues that make them switch from one whim to the other? I'm sure having that kind of control, being able to command those kind of reactions out of another human being, must be a huge factor. But is there something more to it?