"Demonic Abandoning Body Technique" is a self-mutilation technique in the Devil Path that stimulates the body's potential to unleash its greatest power. However, a cultivator's body is their most precious asset, relating to their achievements in cultivation. Once they lose a limb, they will never have the hope of achieving the great Dao.
If Fang Han were to abandon one of his arms, he wouldn't be able to cultivate a Golden Core within sixty years because the consumption of his Yuan Qi would be too severe.
But now the situation was desperate, and Hei You King would die if he didn't mutilate himself. With no other option, he had to sacrifice part of his body and enhance the power of his "Dark Primordial Spirit" to escape first and then deal with the consequences later.
