I wandered over here because something occured to me yesterday while posting in another topic: Sauron probably wanted the seven rings of the Dwarves back because they hadn't had the effect he wanted, but might it not be possible that he took back the Nine because he realized -- especially after he himself lost the One -- that Rings of Power were a double-edged sword in a way he hadn't anticipated? It was said that if Sauron regained the One, then the minds and works of those who held the Three would be laid bare to him. He knew that this would happen, as it was an effect of his original wielding of the One. But once he lost his own Ring, would he not fear that those still in possession of their Rings might turn the tables, and sooner or later, his mind and works would be laid bare to
them? The Witch King, as near as I can tell, while a king of Men before he took his ring, did not become a sorcerer until after Sauron gave him one of the Nine and taught him black arts. The WK became powerful enough to be a fearsome enemy of the Free Peoples in his own right, which was no doubt just fine with Sauron while he still held the Master Ring. Once that was gone... I can just hear the little wheels of paranoia spinning in his mind, worrying that what he had given away and taught might now be a threat to him, that not only would those blasted Elves start working their way into his private thoughts, but even his own mightiest servant might one day realize that he had something he could hold over Sauron, that he might learn secrets that could be used against his master. As the traitor is always afraid of being betrayed, the paranoid always project their own imagined motives and fears onto others. Sauron thus wouldn't necessarily want the lesser Rings back to use himself; he would want them back so that he could be danged certain that those enslaved to their existence could not make any use of them of which he was unaware. That, and he might want them back after they'd made wraiths of their owners so that he could hand them out to the next batch of willing victims and thus conquer them.
Did that make any sense? I hope so, but it's Monday, and the brain is in less than optimal performance mode.